Copper alloy plate and method for producing same

ABSTRACT

A sheet material of a copper alloy has a chemical composition comprising 1.2 to 5.0 wt % of titanium, and the balance being copper and unavoidable impurities, the material having a mean crystal grain size of 5 to 25 μm and (maximum crystal grain size−minimum crystal grain size)/(mean crystal grain size) being 0.20 or less, assuming that the maximum, minimum and mean values of mean values, each of which is the mean value of crystal grain sizes in a corresponding one of a plurality of regions which are selected from the surface of the sheet material at random and which have the same shape and size, are the maximum, minimum and mean crystal grain sizes, respectively, and the material having a crystal orientation satisfying I{420}/I 0 {420}&gt;1.0, assuming that the intensities of X-ray diffraction on the {420} crystal plane of the surface of the material and the standard powder of pure copper are I{420} and I 0 {420}, respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a copper alloy plate, such asa copper alloy sheet, and a method for producing the same. Morespecifically, the invention relates to a plate material, such as a sheetmaterial, of a copper alloy containing titanium (a sheet material of aCu—Ti alloy), which is used as the material of electric and electronicparts, such as connectors, lead frames, relays and switches, and amethod for producing the same.

2. Description of the Prior Art

The materials used for electric and electronic parts, such asconnectors, lead frames, relays and switches, are required to have sucha high strength that the materials can withstand stress applied theretoduring the assembly and operation of electric and electronic apparatusesusing the parts. The materials used for electric and electronic parts,such as connectors, are also required to have an excellent bendingworkability since the parts are generally formed by bending. Moreover,in order to ensure the contact reliability between electric andelectronic parts, such as connectors, the materials used for the partsare required to have an excellent stress relaxation resistance, i.e., aresistance to such a phenomenon (stress relaxation) that the contactpressure between the parts is deteriorated with age.

In recent years, there is a tendency for electric and electronic parts,such as connectors, to be integrated, miniaturized and lightened. Inaccordance therewith, the sheet materials of copper and copper alloysserving as the materials of the parts are required to be thinned, sothat the required strength level of the materials is more severe.Specifically, the 0.2% yield strength of the materials is desired to bethe strength level of not less than 850 MPa, preferably not less than900 MPa, and more preferably not less than 950 MPa.

In accordance with the miniaturization and complicated shape of electricand electronic parts, such as connectors, it is required to improve theprecision of shape and dimension of products manufactured by bending thesheet materials of copper alloys. As the requirements for productsmanufactured by bending the sheet materials of copper alloys, it is notonly important to produce no cracks in the bent portions of theproducts, but it is also important to ensure the precision of shape anddimension of the products. Moreover, there is a problem in that springback occurs in the bending of the sheet materials of copper alloys.Furthermore, the “spring back” means such a phenomenon that the shape ofa final product is not in conformity with the shape of a product workedin a die since the resilient recovery of the product occurs when theproduct is taken off from the die after the working of a sheet material.

In particular, the problem on the spring back is easy to be explicit asthe required strength level of the materials is more severe. Forexample, there are some cases where the shape and dimension of connecterterminals having portions manufactured by box-bending are deviated, sothat the connector terminals can not be used. For that reason, there isrecently often applied a so-called bending after notching wherein asheet material is bent along a notch which is formed by carrying outnotching (working for forming the notch) in a portion of the sheetmaterial. However, in the bending after notching, portions near thenotch portion are work-hardened by notching, so that cracks are easilyproduced in the subsequent bending operation. Therefore, the bendingafter notching is a very severe bending process for materials.

Moreover, the requirements for the stress relaxation resistance ofelectric and electronic parts, such as connectors, are more severe asthe increase of cases where the parts are used in severe environments.For example, the stress relaxation resistance of electric and electronicparts, such as connectors, is particularly important when the parts areused for automobiles in high-temperature environments. Furthermore, thestress relaxation resistance is such a kind of creep phenomenon that thecontact pressure on a spring portion of a material forming electric andelectronic parts, such as connectors, is deteriorated with age in arelatively high-temperature (e.g., 100 to 200° C.) environment even ifit is maintained to be a constant contact pressure at ordinarytemperature. That is, the stress relaxation resistance is such aphenomenon that the stress applied to a metal material is relaxed byplastic deformation produced by the movement of dislocation, which iscaused by the self-diffusion of atoms forming a matrix and the diffusionof the solid solution of atoms, in a state that the stress is applied tothe metal material.

However, there are trade-off relationships between the strength andbending workability of a sheet material of a metal and between thebending workability and stress relaxation resistance thereof,respectively, and conventionally, a sheet material having a goodstrength, bending workability or stress relaxation resistance issuitably chosen in accordance with the use thereof as a material usedfor a current-carrying part, such as a connector.

Among the sheet materials of copper alloys, the sheet materials of Cu—Tialloys have the next highest strength to the sheet materials of Cu—Bealloys and a superior stress relaxation resistance to that of the sheetmaterials of Cu—Be alloys, and are more advantageous than the sheetmaterials of Cu—Be alloys in view of costs and environmental loads. Forthat reason, the sheet materials of Cu—Ti alloys (e.g., C199 (Cu-3.2 wt% of Ti)) are substituted for part of the sheet materials of Cu—Bealloys to be used as connector materials and so forth. However, it isknown that the sheet materials of Cu—Ti alloys have a lower strengththan that of the sheet materials of Cu—Be alloys (e.g., C17200) having ahigh strength if they have the same bending workability as that of thesheet materials of Cu—Be alloys, and that the sheet materials of Cu—Tialloys have an inferior bending workability to that of the sheetmaterials of Cu—Be alloys if they have the same strength as that of thesheet materials of Cu—Be alloys.

As methods for improving the strength of the sheet materials of Cu—Tialloys, there are a method for increasing the content of Ti, and amethod for choosing a high temper material. However, in the method forincreasing the content of Ti, if the concentration of Ti in a sheetmaterial of a Cu—Ti alloy is too high (for example, if the content of T1is not less than 5 wt %), cracks are easily produced in the sheetmaterial during hot rolling and cold rolling, so that the productivityof the sheet material is remarkably deteriorated. In addition, largedeposits are easily produced, so that the sheet material being the finalproduct can not be utilized as a material for general electric andelectronic parts since the bending workability of the sheet material isdeteriorated although the strength thereof is high. On the other hand,in the method for choosing a high temper material, the strength of thesheet material is improved by increasing the rolling reduction beforeand after an ageing treatment, so that the sheet material being thefinal product has anisotropy although the strength thereof is high. Thatis, it is known that the bending workability of the sheet material in adirection perpendicular to a rolling direction (i.e., the bendingworkability of the sheet material in a so-called “bad way” in which thebending axis of the sheet material is parallel to the rolling direction)is remarkably bad, although the bending workability of the sheetmaterial in a direction parallel to the rolling direction (i.e., thebending workability of the sheet material in a so-called “good way” inwhich the bending axis of the sheet material is perpendicular to therolling direction on the rolled surface) is relatively good.

Generally, in order to improve the bending workability of the sheetmaterials of copper alloys, a method for fining the crystal grains ofthe copper alloys is effective. This is the same in the case of thesheet materials of Cu—Ti alloys. However, since the area of grainboundaries existing per a unit volume is increased as the crystal grainsize is decreased, it is caused to promote stress relaxation being akind of creep phenomenon if the crystal grains are fined. In addition,in sheet materials used in relatively high-temperature environments, thediffusion rate along the grain boundaries of atoms is far higher thanthat in the grains, so that there is a problem in that the originalstress relaxation resistance of the sheet materials is deteriorated ifthe crystal grains are extremely fined (e.g., if the crystal grains arefined so as to have a grain size of 5 μm or less).

In particular, the sheet materials of Cu—Ti alloys have characteristicswherein deposits exist mainly in the form of a modulation structure(spinodal structure) in crystal grains, and the amount of deposits ofparticles in the second phase having the function of pinning the growthof recrystallized grains is relatively small, so that a mixed grainstructure is easily caused by a difference in generating time ofrecrystallized grains during a solution treatment. Therefore, it is noteasy to generate uniform and fine crystal grains.

In recent years, as methods for improving the characteristics of thesheet materials of Cu—Ti alloys, there are proposed a method for finingcrystal grains and a method for controlling crystal orientation(texture) (see, e.g., Japanese Patent Laid-Open Nos. 2002-356726,2004-231985, 2006-241573 and 2006-274289).

In Cu—Ti alloys, Ti exists in two forms, one of which is the form of amodulation structure (spinodal structure) having a periodical variationin concentration in a parent phase, and the other of which is the formof an intermetallic compound of Ti and Cu which are particles in thesecond phase (beta phases). The modulation structure is a structurewhich is generated by continuous fluctuation in concentration of Tisolute atoms and which is generated while holding the completeconsistency with the parent phase. The sheet materials of Cu—Ti alloyshaving such a modulation structure are remarkably hardened, and have asmall loss of ductility (bending workability). On the other hand, betaphases are deposits which are sprinkled in usual crystal grains andgrain boundaries. Such beta phases are easily coarsened, and cause aremarkably great loss of ductility of the sheet materials although thefunction of hardening the sheet materials is extremely small by themodulation structure.

That is, in order to obtain the sheet materials of Cu—Ti alloys havingboth of a high strength and a good bending workability, it is effectiveto develop the modulation structure of the sheet materials whilesuppressing the generation of beta phases thereof. In addition, anotherimportant factor influencing on the bending workability of the sheetmaterials of Cu—Ti alloys is the crystal grain size of the alloys. Asthe crystal grain size of the alloys is decreased, the strain due tobending deformation can be dispersed to improve the bending workabilityof the sheet materials.

However, the crystal grain sizes of the sheet materials of Cu—Ti alloysare determined by recrystallization in the final solution treatment, andthere is a problem in that the crystal grains are easily coarsened ifthe generation of beta phases having the function of pinning the growthof recrystallization is suppressed. In addition, the sheet materials ofCu—Ti alloys have such characteristics that the mixed grain structure iseasily caused by a difference in generating time of recrystallizedgrains during a solution treatment. Therefore, it is not easy togenerate uniform and fine crystal grains, so that cracks are easilyproduced near the boundaries of structures having different crystalgrain sizes during bending deformation. Moreover, there is a problem inthat the anisotropy in bending workability is easily caused if therolling reduction before and after an ageing treatment is increased inorder to improve the strength of the sheet materials of Cu—Ti alloys.

As a typical method for fining the crystal grains of the sheet materialof a copper alloy having a chemical composition, there is a method forcarrying out a solution treatment at a temperature of not higher thanthe solid solubility curve (solvus) of the copper alloy having thechemical composition. If the crystal grains of the sheet materials ofCu—Ti alloys are fined by this method, the solid solution of the totalamount of Ti is not formed, and part of Ti is caused to remain as betaphases having the function of pinning. Therefore, although the crystalgrains can be fined, the effect of improvement of bending workabilitydue to the fining of crystal grains is offset by residual beta phases.

For example, in the method disclosed in Japanese Patent Laid-Open No.2002-356726, a solution treatment is carried out at a lower temperaturethan the solid solubility curve of an alloy having a chemicalcomposition by 10 to 60° C., so that the sheet material of a Cu—Ti alloyhaving a 0.2% yield strength of about 900 MPa can be obtained, but theratio R/t of the minimum bending radius R to the thickness t of thesheet material in bending in the bad way remains a relatively greatvalue of about 5.

In the method disclosed in Japanese Patent Laid-Open No. 2004-231985,Fe, Co, Ni and so forth are added to Cu—Ti alloys to form theintermetallic compounds of additional elements, such as Ti and Fe, sothat the intermetallic compounds pin the boundaries of recrystallizedgrains to fine crystal grains in place of beta phases. However, thereare disadvantages in that the development of the modulation structure ofTi is inhibited by the formation of the intermetallic compounds of thethird element, such as Fe, and Ti, so that it is not possible tosufficiently improve the characteristics.

In the method disclosed in Japanese Patent laid-Open No. 2006-241573,the ratio of the intensity of X-ray diffraction on the {220} plane of asheet material to that on the {111} plane thereof is set to beI{220}/I{111}>4 in order to improve the strength and electricconductivity of sheet material. If the rolling texture of the sheetmaterial is adjusted so that the sheet material has a principalorientation component of {220}, it is effective to improve the strengthand electric conductivity of the sheet material. However, it was foundthat the {220} plane was the rolling texture, so that the bendingworkability of the sheet material in the bad way was remarkablydeteriorated.

In the method disclosed in Japanese Patent Laid-Open No. 2006-274289, inorder to improve the bending workability of sheet materials, the textureof the sheet materials is controlled so that the maximum value of theintensities of X-ray diffraction in four regions including {110}<115>,{110}<114> and {110}<113> on a {111} positive pole figure is in therange of from 5.0 to 15.0 (a ratio of intensity to a randomorientation). In addition, in order to obtain such a texture, thecold-rolling reduction is set to be in the range of from 85% to 97%before a solution treatment. Such a texture is a typical alloy-typetexture ({110}<112>-{110}<100>), and the {111} positive pole figurethereof is similar to the {111} positive pole figure of 70/30 brass(see, e.g., “Metal Data Book”, third revision, p 361, edited by JapanSociety for Metals, published by Maruzen Corporation). Thus, in theconventional method for adjusting the distribution in crystalorientation on the basis of the typical texture, it is difficult togreatly improve the bending workability of the sheet materials. In theabove-described method disclosed in Japanese Patent Laid-Open No.2006-274289, it is possible to obtain a sheet material of a Cu—Ti alloyhaving a 0.2% yield strength of about 870 MPa, but the ratio R/t of theminimum bending radius R to the thickness t of the sheet material inbending remains a relatively great value of about 1.6.

In order to improve the precision of shape and dimension of productsmanufactured by bending, it is effective to use the bending afternotching for the sheet materials of copper alloys. However, in the sheetmaterials of Cu—Ti alloys wherein crystal grains and textures arecontrolled by the above-described methods disclosed in Japanese PatentLaid-Open Nos. 2002-356726, 2004-231985, 2006-241573 and 2006-274289, itwas not considered to prevent cracks from being produced by the bendingafter notching, so that it was found that the bending workability afternotching was not sufficiently improved.

In the sheet materials of Cu—Ti alloys, there is also a problem in thatit is difficult to ensure the precision of shape and dimension ofproducts, which are manufactured by bending, due to spring back. Thebending after notching is effective in order to reduce spring back. Inthe bending after notching, portions near the notched portion arework-hardened by notching, so that cracks are easily produced in thesubsequent bending. For that reason, in the sheet materials of Cu—Tialloys, the bending after notching has not been adopted industrially inthe present circumstances.

Moreover, if crystal grains are fined as described above, it isdisadvantageous in order to overcome a stress relaxation being a kind ofcreep phenomenon although it is effective in order to improve thebending workability of the sheet materials to some extent. Thus, it isdifficult to improve the stress relaxation resistance of the sheetmaterials in circumstances where it is difficult to sufficiently improvethe bending workability thereof.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to eliminate theaforementioned problems and to provide a sheet material of a Cu—Ti alloyhaving an excellent bending workability, such as an excellent bendingworkability after notching, and an excellent stress relaxationresistance while maintaining a high strength, and a method for producingthe same.

In order to accomplish the aforementioned and other objects, theinventors have diligently studied and found that it is possible toproduce a sheet material of a Cu—Ti alloy having an excellent bendingworkability, such as an excellent bending workability after notching,and an excellent stress relaxation resistance while maintaining a highstrength, if the sheet material of a copper alloy has a chemicalcomposition comprising 1.2 to 5.0 wt % of titanium, and the balancebeing copper and unavoidable impurities, and if the sheet material has amean crystal grain size of 5 to 25 μm, and (maximum crystal grainsize−minimum crystal grain size)/(mean crystal grain size) being notgreater than 0.20, assuming that the maximum value of mean values, eachof which is the mean value of crystal grain sizes in a corresponding oneof a plurality of regions which are selected from a surface of the sheetmaterial of the copper alloy at random and which have the same shape andsize, is the maximum crystal grain size, that the minimum value of themean values is the minimum crystal grain size and that the mean value ofthe mean values is the mean crystal grain size, and if the sheetmaterial has a crystal orientation which satisfies I{420}/I₀{420}>1.0,assuming that the intensity of X-ray diffraction on the {420} crystalplane on the surface of the sheet material of the copper alloy is I{420}and that the intensity of X-ray diffraction on the {420} crystal planeof the standard powder of pure copper is I₀{420}. Thus, the inventorshave made the present invention.

According one aspect of the present invention, there is provided a sheetmaterial of a copper alloy having a chemical composition comprising 1.2to 5.0 wt % of titanium, and the balance being copper and unavoidableimpurities, wherein the sheet material of the copper alloy has a meancrystal grain size of 5 to 25 μm, and (maximum crystal grainsize−minimum crystal grain size)/(mean crystal grain size) is notgreater than 0.20, assuming that the maximum value of mean values, eachof which is the mean value of crystal grain sizes in a corresponding oneof a plurality of regions which are selected from a surface of the sheetmaterial of the copper alloy at random and which have the same shape andsize, is the maximum crystal grain size, that the minimum value of themean values is the minimum crystal grain size and that the mean value ofthe mean values is the mean crystal grain size, and wherein the sheetmaterial of the copper alloy has a crystal orientation which satisfiesI{420}/I₀{420}>1.0, assuming that the intensity of X-ray diffraction onthe {420} crystal plane on the surface of the sheet material of thecopper alloy is I{420} and that the intensity of X-ray diffraction onthe {420} crystal plane of the standard powder of pure copper isI₀{420}.

In this sheet material of the copper alloy, the crystal orientation ofthe sheet material of the copper alloy preferably satisfiesI{220}/I₀{220}≦4.0, assuming that the intensity of X-ray diffraction onthe {220} crystal plane on the surface of the sheet material of thecopper alloy is I{220} and that the intensity of X-ray diffraction onthe {220} crystal plane of the standard powder of pure copper isI₀{220}.

The chemical composition of the sheet material of the copper alloy mayfurther comprise one or more elements which are selected from the groupconsisting of 1.5 wt % or less of nickel, 1.0 wt % or less of cobalt and0.5 wt % or less of iron.

The chemical composition of the sheet material of the copper alloy mayfurther comprise one or more elements which are selected from the groupconsisting of 1.2 wt % or less of tin, 2.0 wt % or less of zinc, 1.0 wt% or less of magnesium, 1.0 wt % or less of zirconium, 1.0 wt % or lessof aluminum, 1.0 wt % or less of silicon, 0.1 wt % or less ofphosphorus, 0.05 wt % or less of boron, 1.0 wt % or less of chromium,1.0 wt % or less of manganese, 1.0 wt % or less of vanadium, 1.0 wt % orless of silver, 1.0 wt % or less of beryllium and 1.0 wt % or less ofmisch metal, the total amount of these elements being 3 wt % or less.

The sheet material of the copper alloy preferably has a 0.2% yieldstrength of 850 MPa or more. If the 90° W bending test of a first testpiece, which is cut off from the sheet material of the copper alloy sothat the longitudinal direction of the first test piece is the rollingdirection LD of the sheet material of the copper alloy, is carried outso that the bending axis of the first test piece is a direction TDperpendicular to the rolling direction and thickness direction of thefirst test piece, and if the 90° W bending test of a second test piece,which is cut off from the sheet material of the copper alloy so that thelongitudinal direction of the second test piece is the TD, is carriedout so that the bending axis of the second test piece is the LD, theratio R/t of the minimum bending radius R to the thickness t of each ofthe first and second test pieces is preferably 1.0 or less.

According to another aspect of the present invention, there is provideda method for producing a sheet material of a copper alloy, the methodcomprising the steps of: melting and casting raw materials of a copperalloy to form an ingot, the copper alloy having a chemical compositionwhich consists of: 1.2 to 5.0 wt % of titanium; optionally one or moreelements which are selected from the group consisting of 1.5 wt % orless of nickel, 1.0 wt % or less of cobalt and 0.5 wt % or less of iron;optionally one or more elements which are selected from the groupconsisting of 1.2 wt % or less of tin, 2.0 wt % or less of zinc, 1.0 wt% or less of magnesium, 1.0 wt % or less of zirconium, 1.0 wt % or lessof aluminum, 1.0 wt % or less of silicon, 0.1 wt % or less ofphosphorus, 0.05 wt % or less of boron, 1.0 wt % or less of chromium,1.0 wt % or less of manganese, 1.0 wt % or less of vanadium, 1.0 wt % orless of silver, 1.0 wt % or less of beryllium and 1.0 wt % or less ofmisch metal, the total amount of these elements being 3 wt % or less;and the balance being copper and unavoidable impurities; hot-rolling theingot in a temperature range of from 950° C. to 500° C. to form a plateof the copper alloy, by hot-rolling the ingot at a rolling reduction ofnot less than 30% in a temperature range of from less than 700° C. to500° C. after carrying out an initial rolling pass in a temperaturerange of from 950° C. to 700° C.; cold-rolling the plate of the copperalloy at a rolling reduction of not less than 85%; carrying out asolution treatment which holds the plate of the copper alloy in atemperature range of from 750° C. to 1000° C. for 5 seconds to 5minutes; cold-rolling the plate of the copper alloy at a rollingreduction of 0 to 50% after the solution treatment; ageing thecold-rolled plate of the copper alloy, which is cold-rolled after thesolution treatment, at a temperature of 300 to 550° C.; and finishcold-rolling the aged plate of the copper alloy at a rolling reductionof 0 to 30%.

In this method for producing a sheet material of a copper alloy, theingot is preferably hot-rolled at a rolling reduction of not less than60% in the temperature range of from 950° C. to 700° C. The rollingreduction in cold-rolling between the hot-rolling and the solutiontreatment is preferably not less than 90%. The solution treatment ispreferably carried out by a heat treatment which holds the plate of thecopper alloy at a higher temperature than a solid solubility curve ofthe copper alloy by 30° C. or more, in the temperature range of from750° C. to 1000° C. for a holding period of time which is adjusted sothat the mean crystal grain size of the sheet material of the copperalloy after the solution treatment is in the range of from 5 μm to 25μm.

In the method for producing a sheet material of a copper alloy, assumingthat the ageing temperature capable of obtaining the maximum hardness inthe chemical composition of the copper alloy is T_(M) (° C.) and thatthe maximum hardness thereof is H_(M) (HV), the ageing temperature inthe ageing treatment is preferably set to be a temperature which isT_(M)±10° C. in the temperature range of from 300° C. to 550° C., andthe ageing time in the ageing treatment is preferably set so that thehardness of the plate of the copper alloy is in the range of from 0.90H_(M) to 0.95 H_(M) after the ageing treatment.

In the method for producing a sheet material of a copper alloy, a lowtemperature annealing operation may be carried out at a temperature of150 to 450° C. after the finish cold rolling.

According to a further aspect of the present invention, there isprovided a connector terminal using the above-described sheet materialof a copper alloy as a material thereof.

Throughout the specification, the “maximum crystal grain size” means themaximum value of mean values, each of which is the mean value of crystalgrain sizes in a corresponding one of a plurality of regions selectedfrom the surface (rolled surface) of a sheet material of a copper alloyat random, the plurality of regions having the same shape and size. Forexample, from the optical microphotograph of the surface (rolledsurface) of a sheet material of a copper alloy, ten square visual fieldshaving a size of 100 μm×100 μm are selected at random, two sides of eachof the visual fields being parallel to the rolling direction (LD) andthe other two sides of each of the visual fields being parallel to adirection (TD) perpendicular to the rolling direction. In each of thevisual fields, crystal grain sizes are measured by the method of sectionbased on JIS H0501. Then, the mean values d₁, d₂, . . . , d₁₀ of thecrystal grain sizes in the visual fields are calculated, respectively.The maximum value of the mean values thus calculated is the maximumcrystal grain size. The “minimum crystal grain size” means the minimumvalue of the mean values of crystal grain sizes in the above-describedregions. For example, the “minimum crystal grain size” means the minimumvalue of the mean values d₁, d₂, . . . , d₁₀ of the crystal grain sizesin the visual fields. The “mean crystal grain size” means the mean valueof the mean values of crystal grain sizes in the above-describedregions. For example, the “mean crystal grain size” means the mean valued_(mean) (=(d₁=d₂+ . . . +d₁₀)/10) of the mean values d₁, d₂, . . . ,d₁₀ of the crystal grain sizes in the visual fields. Furthermore, thecrystal grain sizes in each of the visual fields can be obtained bymeasuring the length of each of crystal grains, which are completely cutby line segments extending in a direction (TD) perpendicular to therolling direction and having a length of 100 μm, by the method ofsection based on JIS H0501.

According to the present invention, it is possible to provide a sheetmaterial of a Cu—Ti alloy having an excellent bending workability, suchas an excellent bending workability after notching, and an excellentstress relaxation resistance while maintaining a high strength, and amethod for producing the same.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given herebelow and from the accompanying drawings of thepreferred embodiments of the invention. However, the drawings are notintended to imply limitation of the invention to a specific embodiment,but are for explanation and understanding only.

In the drawings:

FIG. 1 is a standard reversed pole figure which shows the Schmid factordistribution of a face-centered cubic crystal;

FIG. 2 is a sectional view schematically showing the section of a jigfor forming a notch;

FIG. 3 is a perspective view for explaining a notching method;

FIG. 4 is a sectional view schematically showing the section of portionsnear a notch forming portion of a notched bending test piece;

FIG. 5A is an optical microphotograph showing the structure of thesurface of a sheet material of a copper alloy before a solutiontreatment in Example 1;

FIG. 5B is an optical microphotograph showing the structure of thesurface of the sheet material of the copper alloy after the solutiontreatment at 850° C. for 10 seconds in Example 1;

FIG. 5C is an optical microphotograph showing the structure of thesurface of the sheet material of the copper alloy after the solutiontreatment at 850° C. for 30 seconds in Example 1;

FIG. 5D is an optical microphotograph showing the structure of thesurface of the sheet material of the copper alloy after the solutiontreatment at 850° C. for 60 seconds in Example 1;

FIG. 6A is an optical microphotograph showing the structure of thesurface of a sheet material of a copper alloy before a solutiontreatment in Comparative Example 1;

FIG. 6B is an optical microphotograph showing the structure of thesurface of the sheet material of the copper alloy after the solutiontreatment at 850° C. for 10 seconds in Comparative Example 1;

FIG. 6C is an optical microphotograph showing the structure of thesurface of the sheet material of the copper alloy after the solutiontreatment at 850° C. for 30 seconds in Comparative Example 1; and

FIG. 6D is an optical microphotograph showing the structure of thesurface of the sheet material of the copper alloy after the solutiontreatment at 850° C. for 60 seconds in Comparative Example 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiment of a sheet material of a copper alloy accordingto the present invention has a chemical composition consisting of: 1.2to 5.0 wt % of titanium (Ti); optionally one or more elements which areselected from the group consisting of 1.5 wt % or less of nickel (Ni),1.0 wt % or less of cobalt (Co) and 0.5 wt % or less of iron (Fe);optionally one or more elements which are selected from the groupconsisting of 1.2 wt % or less of tin (Sn), 2.0 wt % or less of zinc(Zn), 1.0 wt % or less of magnesium (Mg), 1.0 wt % or less of zirconium(Zr), 1.0 wt % or less of aluminum (Al), 1.0 wt % or less of silicon(Si), 0.1 wt % or less of phosphorus (P), 0.05 wt % or less of boron(B), 1.0 wt % or less of chromium (Cr), 1.0 wt % or less of manganese(Mn), 1.0 wt % or less of vanadium (V), 1.0 wt % or less of silver (Ag),1.0 wt % or less of beryllium (Be) and 1.0 wt % or less of misch metal,the total amount of these elements being 3 wt % or less; and the balancebeing copper and unavoidable impurities.

The sheet material of the copper alloy has a mean crystal grain size of5 to 25 μm, wherein (maximum crystal grain size−minimum crystal grainsize)/(mean crystal grain size) is not greater than 0.20, assuming thatthe maximum value of mean values, each of which is the mean value ofcrystal grain sizes in a corresponding one of a plurality of regionsselected from the surface of the sheet material of the copper alloy atrandom, the regions having the same shape and size, is the maximumcrystal grain size, that the minimum value of the above-described meanvalues is the minimum crystal grain size and that the mean value of theabove-described mean values is the mean crystal grain size.

The sheet material of the copper alloy has a crystal orientation whichsatisfies I{420}/I₀{420}>1.0, assuming that the intensity of X-raydiffraction on the {420} crystal plane on the surface of the sheetmaterial of the copper alloy is I{420} and that the intensity of X-raydiffraction on the {420} crystal plane of the standard powder of purecopper is I₀{420}, and which satisfies I{220}/I₀{220}≦4.0, assuming thatthe intensity of X-ray diffraction on the {220} crystal plane on thesurface of the sheet material of the copper alloy is I{220} and that theintensity of X-ray diffraction on the {220} crystal plane of thestandard powder of pure copper is I₀{220}.

The sheet material of the copper alloy preferably has a 0.2% yieldstrength of 850 MPa or more in the LD (rolling direction) thereof. Thesheet material of the copper alloy preferably has such a bendingworkability that the ratio R/t of the minimum bending radius R, at whichcracks are not produced in the 90° W bending test based on JIS H3110, tothe thickness t of the sheet material is 1.0 or less in each of the LDand TD (the direction perpendicular to the rolling direction andthickness direction) thereof.

[Composition of Alloy]

The sheet material of the copper alloy according to the presentinvention is a sheet material of a Cu—Ti alloy containing Cu and Ti,preferably an alloy consisting of two elements of Cu and Ti. The sheetmaterial of the copper alloy may optionally contain a small amount ofother elements, such as Ni, Co and Fe.

Titanium (Ti) is an element having an excellent age hardening functionin a Cu matrix, and contributes to the improvement of the strength andstress relaxation resistance of the sheet material of the copper alloy.In a plate of a Cu—Ti alloy, a supersaturated solid solution isgenerated by a solution treatment. Then, if ageing is carried out at alower temperature, a modulation structure (spinodal structure), which isa metastable phase, is developed. Then, if ageing is continued, stablephases (beta phases) are generated. The modulation structure does notrequire any nucleation, dislike usual deposits generated by nucleationand growth. The modulation structure is a structure which is generatedby continuous fluctuation in concentration of solute atoms and which isgenerated while holding the complete consistency with the parent phase.At the developmental stage of the modulation structure, the sheetmaterial of the Cu—Ti alloy is remarkably hardened, and has a small lossof ductility. On other hand, the stable phases (beta phases) aredeposits which are sprinkled in usual crystal grains and grainboundaries. The stable phases are easily coarsened, and cause a greatloss of ductility of the sheet material although the function ofhardening the sheet material is smaller than that in the modulationstructure which is a metastable phase.

Therefore, the strength of the sheet material of the Cu—Ti alloy ispreferably enhanced by the metastable phases as many as possible, whilesuppressing the generation of the stable phases (beta phases). If thecontent of Ti is less than 1.2 wt %, it is difficult to sufficientlyobtain the function of strengthening the sheet material by themetastable phases. On the other hand, if the content of Ti exceeds 5.0wt % to be excessive, the stable phases (beta phases) are easilygenerated, and cracks are easily produced in hot working and coldworking, so that the productivity of the sheet material is easilydeteriorated. In addition, the temperature range capable of carrying outa solution treatment is caused to be narrow, so that it is difficult tocause the sheet material of the Cu—Ti alloy to have goodcharacteristics. Therefore, the content of Ti is preferably in the rangeof from 1.2 wt % to 5.0 wt %, more preferably in the range of from 2.0wt % to 4.0 wt %, and most preferably in the range of from 2.5 wt % to3.5 wt %.

Nickel (Ni), cobalt (Co) and iron (Fe) are elements which formintermetallic compounds with Ti to contribute to the improvement of thestrength of the sheet material of the copper alloy. At least one ofthese elements may be optionally added to the copper alloy. Inparticular, since the intermetallic compounds inhibit crystal grainsfrom being coarsened in the solution treatment of Cu—Ti alloys, thesolution treatment can be carried out at a higher temperature, so thatthe addition of Ni, Co and Fe is advantageous in order to sufficientlygenerate the solid solution of Ti. However, if the contents of Fe, Coand Ni are excessive, the amount of Ti consumed by the generation of theintermetallic compounds is increased, so that the amount of Ti to beformed as the solid solution is necessarily decreased to easily lowerthe strength of the sheet material. Therefore, if Ni, Co and Fe areadded to the copper alloy, the content of Ni is preferably 1.5 wt % orless, more preferably in the range of from 0.05 wt % to 1.5 wt %, andmost preferably in the range of from 0.1 wt % to 1.0 wt %, the contentof Co is preferably 1.0 wt % or less, more preferably in the range offrom 0.05 wt % to 1.0 wt %, and most preferably in the range of from 0.1wt % to 0.5 wt %, and the content of Fe is preferably 0.5 wt % or less,more preferably in the range of from 0.05 wt % t 0.5 wt %, and mostpreferably in the range of from 0.1 wt % to 0.3 wt %.

Tin (Sn) has the functions of carrying out the solid-solutionstrengthening (or hardening) of the copper alloy and of improving thestress relaxation resistance of the sheet material thereof. In order tosufficiently provide these functions, the content of Sn is preferably0.1 wt % or more. However, if the content of Sn exceeds 1.0 wt %, thecastability and electric conductivity of the copper alloy are remarkablylowered. Therefore, if the copper alloy contains Sn, the content of Snis preferably in the range of from 0.1 wt % to 1.0 wt %, and morepreferably in the range of from 0.1 wt % to 0.5 wt %.

Zinc (Zn) has the function of improving the castability of the copperalloy, in addition to the function of improving the solderability andstrength thereof. In order to sufficiently provide these functions, thecontent of Zn is preferably 0.1 wt % or more. If the copper alloycontains Zn, inexpensive brass scraps may be used. However, if thecontent of Zn exceeds 2.0 wt %, the electric conductivity and stresscorrosion cracking resistance of the sheet material of the copper alloyare easily deteriorated. Therefore, if the copper alloy contains Zn, thecontent of Zn is preferably in the range of from 0.1 wt % to 2.0 wt %,and more preferably in the range of from 0.3 wt % to 1.0 wt %.

Magnesium (Mg) has the function of improving the stress relaxationresistance of the sheet material of the copper alloy, and the functionof desulfurizing the sheet material of the copper alloy. In order tosufficiently provide these functions, the content of Mg is preferably0.01 wt % or more. However, Mg is an element which is easily oxidized,and the castability of the copper alloy is remarkably deteriorated ifthe content of Mg exceeds 1.0 wt %. Therefore, if the copper alloycontains Mg, the content of Mg is preferably in the range of from 0.01wt % to 1.0 wt %, and more preferably in the range of from 0.1 wt % to0.5 wt %.

As other elements, the copper alloy may optionally contain at least oneelement which is selected from the group consisting 1.0 wt % or less ofZr, 1.0 wt % or less of Al, 1.0 wt % or less of Si, 0.1 wt % or less ofP, 0.05 wt % or less of B, 1.0 wt % or less of Cr, 1.0 wt % or less ofMn, 1.0 wt % or less of V, 1.0 wt % or less of Ag, 1.0 wt % or less ofBe, and 1.0 wt % or less of misch metal. For example, Zr and Al can formintermetallic compounds with Ti, and Si can generate deposits with Ti.In addition, Cr, Zr, Mn and V are easy to form high melting pointcompounds with S, Pb and so forth, which exist as unavoidable impuritiesin the copper alloy, and Cr, B, P, Zr and misch metal (a mixture of rareearth elements containing Ce, La, Dy, Nd, Y and so forth) have thefunction of fining the cast structure of the copper alloy to contributeto the improvement of the hot workability thereof. Moreover, Ag andBehave the function of improving the strength of the sheet material ofthe copper alloy without greatly deteriorating the electric conductivitythereof.

If the copper alloy contains at least one element which is selected fromthe group consisting of Zr, Al, Si, P, B, Cr, Mn, V, Ag, Be and mischmetal, the total amount of these elements is preferably 0.01 wt % ormore in order to sufficiently provide the function of each element.However, if a large amount of these elements are contained in the copperalloy, the elements have a bad influence on the hot workability and coldworkability thereof, and it is unfavorable with respect to costs.Therefore, the total amount of Sn, Zn, Mg, Zr, Al, Si, P, B, Cr, Mn, V,Ag, Be and misch metal is preferably 3 wt % or less, and more preferably2 wt % or less, and more preferably 1 wt % or less, and most preferably0.5 wt % or less.

[Mean Crystal Grain Size]

The decrease of the mean crystal grain size of the copper alloy isadvantageous to improve the bending workability of the sheet materialthereof. However, in Cu—Ti alloys, there is a problem in that betaphases are easy to remain as crystal grains are fined. If the meancrystal grain size of the copper alloy is too small, the stressrelaxation resistance of the sheet material thereof is easy todeteriorate. If the mean crystal grain size of the copper alloy is notless than 5 μm, preferably not less than 8 μm, it is easy to ensure thestress relaxation resistance of the sheet material thereof to such anextent that the sheet material thereof can be satisfactorily used as thematerial of connectors for automobiles. The mean crystal grain size ofthe copper alloy is more preferably not less than 10 μm. However, if themean crystal grain size of the copper alloy is too large, the surface ofthe bent portion of the sheet material thereof is easy to be rough, sothat there are some cases where the bending workability of the sheetmaterial thereof is deteriorated. Therefore, the mean crystal grain sizeof the copper alloy is preferably not greater than 25 μm, morepreferably not greater than 20 μm, and most preferably not greater than15 μm. The final mean crystal grain size of the copper alloy is roughlydetermined by crystal grain sizes at a stage after a solution treatment.Therefore, the control of the mean crystal grain size of the copperalloy can be carried out by adjusting solution treatment conditions.

[Crystal Grain Size Distribution]

Cu—Ti alloys have such characteristics that a mixed grain structure iseasily produced by a difference in time for generating recrystallizedgrains in a solution treatment, so that cracks are easily produced nearthe boundaries of structures having different crystal grain sizes duringbending deformation. For that reason, (maximum crystal grainsize−minimum crystal grain size)/(mean crystal grain size), whichindicates the uniformity of crystal grains, is preferably not greaterthan 0.20 and more preferably not greater than 0.15, assuming that themaximum value of mean values, each of which is the mean value of crystalgrain sizes in a corresponding one of a plurality of regions which areselected from the surface of the sheet material of the copper alloy atrandom and which have the same shape and size, is the maximum crystalgrain size, that the minimum value of the above-described mean values isthe minimum crystal grain size and that the mean value of theabove-described mean values is the mean crystal grain size.

[Texture]

The pattern of X-ray diffraction from the surface (rolled surface) ofthe sheet material of a Cu—Ti alloy generally comprises the peaks ofdiffraction on four crystal planes of {111}, {200}, {220} and {311}. Theintensities of X-ray diffraction from other crystal planes are farsmaller than those from the four crystal planes. In the sheet materialsof Cu—Ti alloys manufactured by usual manufacturing processes, theintensity of X-ray diffraction from the {420} plane is negligibly weak.The preferred embodiment of a method for producing a sheet material of acopper alloy according to the present invention can produce a sheetmaterial of a Cu—Ti alloy having a texture wherein the {420} plane is aprincipal orientation component. It was found that the strongerdevelopment of the texture is advantageous in order to improve thebending workability of the sheet material as follows.

There are Schmid factors as indexes which indicate the probability ofgenerating plastic deformation (slip) when an external force is appliedto a crystal in a certain direction. Assuming that the angle between thedirection of the external force applied to the crystal and the normalline to the slip plane is φ and that the angle of the direction of theexternal force applied to the crystal and the slip direction is λ, theSchmid factors are expressed by cos φ·cos λ, and the values thereof arenot greater than 0.5. If the Schmid factor is greater (i.e., if theSchmid factor approaches 0.5), it means that shearing stress in slipdirections is greater. Therefore, if the Schmid factor is greater (i.e.,if the Schmid factor approaches 0.5) when an external force is appliedto a crystal in a certain direction, the crystal is easily deformed. Thecrystal structure of Cu—Ti alloys is face centered cubic (fcc). The slipsystem of a face-centered cubic crystal has a slip plane of {111} and aslip direction of <110>. It is known that an actual crystal is easilydeformed to decrease the extent of work hardening as the Schmid factoris greater.

FIG. 1 is a standard reversed pole figure which shows the Schmid factordistribution of a face-centered cubic crystal. As shown in FIG. 1, theSchmid factor in the <120> direction is 0.490 which is close to 0.5.That is, a face-centered cubic crystal is very easy to be deformed if anexternal force is applied to the crystal in the <120> direction. TheSchmid factors in other directions are 0.408 in the <100> direction,0.445 in the <113> direction, 0.408 in the <110> direction, 0.408 in the<112> direction, and 0.272 in the <111> direction.

The texture having a principal orientation component of {420} means sucha texture that the existing rate of crystals is high, the {420} plane,i.e., the {210} plane, of the crystals being substantially parallel tothe surface (rolled surface) of the sheet material. In crystals having aprincipal orientation plane of {210}, the direction (ND) perpendicularto the surface of the sheet material is the <120> direction, and theSchmid factor thereof is close to 0.5. Therefore, the crystals areeasily deformed in the direction ND, and the extent of work hardening issmall. On other hand, a typical rolling texture of Cu—Ti alloys has aprincipal orientation component of {220}. In this case, the existingrate of crystals is high, the {220} plane, i.e., the {110} plane, of thecrystals is substantially parallel to the surface (rolled surface) ofthe sheet material. In the crystals having a principal orientation planeof {110}, the direction ND is the <110> direction, and the Schmid factorthereof is about 0.4, so that the extent of work hardening caused bydeformation in the direction ND is greater than that in crystals havinga principal orientation plane of {210}. In addition, a typicalrecrystallized texture of Cu—Ti alloys has a principal orientationcomponent of {311}. In crystals having a principal orientation plane of{311}, the direction ND is the <113> direction, and the Schmid factorthereof is about 0.45, so that the extent of work hardening caused bydeformation in the direction ND is greater than that in crystals havinga principal orientation plane of {210}.

In the bending after notching, the extent of work hardening caused bydeformation in the direction ND is extremely important, because notchingis deformation in the direction ND, and because the extent of workhardening in portions of the sheet material, the thickness of which isdecreased by notching, greatly controls the bending workability of thesheet material when the sheet material is subsequently bent along anotch. Assuming that the intensity of X-ray diffraction on the {420}crystal plane on the surface of the sheet material of the copper alloyis I{420} and that the intensity of X-ray diffraction on the {420}crystal plane of the standard powder of pure copper is I₀{420}, in thecase of such a texture having a principal orientation component of {420}that I{420}/I₀{420}>1.0 is satisfied, the extent of work hardeningcaused by notching is smaller than that in the rolling texture orrecrystallized texture of conventional Cu—Ti alloys, so that the bendingworkability after notching is remarkably improved.

In addition, in the case of such a texture having a principalorientation component of {420} that I{420}/I₀{420}>1.0 is satisfied,crystals having a principal orientation plane of {210} have the <120>and <100> directions as other directions on the surface of the sheetmaterial, i.e., on the {210} plane, and these directions areperpendicular to each other. In fact, the LD is the <100> direction, andthe TD is the <120> direction. As an example of crystal orientation, incrystals having a principal orientation plane of (120), the LD is the[011] direction, and the TD is [−2,1,0] direction. The Schmid factors insuch crystals are 0.408 in the LD and 0.490 in the TD. On the otherhand, in a typical rolling texture of Cu—Ti alloys, the principalorientation plane is the {110} plane, the LD is the <112> direction, andthe TD is the <111> direction, the Schmid factors on the surface of thesheet material being 0.408 in the LD and 0.272 in the TD. In a typicalrecrystallized texture of Cu—Ti alloys, the principal orientation planeis the {113} plane, the LD is the <112> direction, and the TD is the<110> direction, the Schmid factors on the surface of the sheet materialbeing 0.408 in the LD and 0.408 in the TD. If the Schmid factors in theLD and TD are thus considered, deformation on the surface of the sheetmaterial having a texture having a principal orientation component of{420} is easier than that on the surface of a sheet material having therolling texture or recrystallized texture of conventional Cu—Ti alloys.It is considered that this point is advantageous in order to preventcracks from being produced in the bending after notching.

When the bending of a sheet material of a metal is carried out, thecrystal grains of the metal are not uniformly deformed, and there arecrystal grains, which are easily deformed during bending, and crystalgrains which are difficult to be deformed during bending, since thecrystal orientations of the crystal grains are different from eachother. As the extent of bending is increased, the crystal grains beingeasily deformed are deformed in preference to other crystal grains, andfine irregularities are produced on the surface of the bent portion ofthe metal sheet by non-uniform deformation between crystal grains. Theseirregularities are developed to form wrinkles, and to produce cracks(breaks) according to circumstances. As described above, in a sheetmaterial of a metal having such a texture that I{420}/I₀{420}>1.0 issatisfied, crystal grains are easily deformed in the ND and on thesurface of the sheet material, in comparison with sheet materials havingusual textures. Thus, it is considered that the bending workabilityafter notching and the usual bending workability are remarkably improvedeven if crystal grains are not particularly fined.

Such a crystal orientation satisfies I{420}/I₀{420}>1.0, assuming thatthe intensity of X-ray diffraction on the {420} crystal plane on thesurface of the sheet material of the copper alloy is I{420} and that theintensity of X-ray diffraction on the {420} crystal plane of thestandard powder of pure copper is I₀{420}. Since reflection does notoccur on the {210} plane although it occurs on the {420} plane in thepattern of X-ray diffraction of a face-centered cubic crystal, thecrystal orientation on the {210}plane is evaluated by reflection on the{420} plane.

The texture having a principal orientation component of {420} is formedas a recrystallized texture by a solution treatment. However, in orderto enhance the strength of the sheet material of the copper alloy, thecold rolling of the sheet material of the copper alloy is preferablycarried out after the solution treatment. As the cold-rolling reductionis increased, a rolling texture having a principal orientation componentof {220} is developed. As the density of orientation of {220} isincreased, the density of orientation of {420} is decreased, but thecold-rolling reduction may be adjusted so as to maintainI{420}/I₀{420}>1.0. However, since there are some cases where theworkability of the sheet material of the copper alloy is deteriorated ifthe texture having a principal orientation component of {220} isexcessively developed, I{220}/I₀{220}≦4.0 is preferably satisfied,assuming that the intensity of X-ray diffraction on the {220} crystalplane on the surface of the sheet material of the copper alloy is I{220}and that the intensity of X-ray diffract ion on the {220} crystal planeof the standard powder of pure copper is I₀{220}. In order to furtherimprove both of the strength and bending workability of the sheetmaterial of the copper alloy, 1.0≦I{220}/I₀{220}≦3.0 is preferablysatisfied.

In the sheet material of the copper alloy having such a specific crystalorientation, the high strength inherent in the sheet material of thecopper alloy is maintained, and it is not required to extremely finecrystal grains in order to improve the bending workability thereof, sothat it is possible to sufficiently provide the function of improvingthe stress relaxation resistance thereof by adding Ti.

[Characteristics]

In order to further miniaturize and thin electric and electronic parts,such as connectors, using the sheet materials of Cu—Ti alloys, the 0.2%yield strength of the sheet materials is preferably not less than 850MPa, more preferably not less than 900 MPa, and most preferably not lessthan 950 MPa. The sheet materials of copper alloys having such strengthcharacteristics can be produced from the raw materials of copper alloyshaving the above-described chemical compositions by a producing methodwhich will be described later.

As the evaluation of the usual bending workability of the sheet materialof the copper alloy, the ratio R/t of the minimum bending radius R tothickness t of the sheet material in the 90° W bending test ispreferably 1.0 or less, more preferably 0.5 or less, in each of the LDand TD. In order to further improve the precision of shape and dimensionof products manufactured by bending the sheet materials of copperalloys, the ratio R/t is preferably 0, i.e., no cracks preferablyappear, as the evaluation of the bending workability after notching inthe LD. Furthermore, the bending workability in the LD is the bendingworkability evaluated by a test piece which is so cut that the LD is thelongitudinal direction (it is the same in the case of the bendingworkability after notching), and the bending axis in the test is the TD.Similarly, the bending workability in the TD is the bending workabilityevaluated by a test piece which is so cut that the TD is thelongitudinal direction, and the bending axis in the test is the LD.

When the sheet materials of copper alloys are used as the materials ofconnectors for automobiles, the stress relaxation resistance in the TDis particularly important, so that the stress relaxation resistance ispreferably evaluated by a stress relaxation rate using a test piecewhich is so cut that the TD is the longitudinal direction. The stressrelaxation rate of the sheet material of the copper alloy is preferably5% or less, and more preferably 3% or less, when the sheet material isheld at 200° C. for 1000 hours, as a method for evaluating the stressrelaxation resistance.

[Producing Method]

The above-described sheet material of the copper alloy can be producedby the preferred embodiment of a sheet material of a copper alloyaccording to the present invention. The preferred embodiment of a sheetmaterial of a copper alloy according to the present invention comprises:a melting and casting step of melting and casting the raw materials of acopper alloy having the above-described composition; a hot rolling stepof carrying out an initial rolling pass in a temperature range of from950° C. to 700° C. and carrying out a hot rolling operation at a rollingreduction of not less than 30% in a temperature range of from less than700° C. to 500° C. to form a plate of the copper alloy, after themelting and casting step; a first cold rolling step of carrying out acold rolling operation at a rolling reduction of not less than 85%,after the hot rolling step; a solution treatment step of carrying out asolution treatment which holds the plate of the copper alloy at atemperature of 750 to 1000° C. for 5 seconds to 5 minutes, after thefirst cold rolling step; a second cold rolling step of carrying out acold rolling operation at a rolling reduction of 0 to 50%, after thesolution treatment step; an ageing treatment step of carrying out anageing treatment at a temperature of 300 to 550° C., after the secondcold rolling step; a finish cold rolling step of carrying out a finishcold rolling operation at a rolling reduction of 0 to 30%, after theageing treatment step; and optionally, a low temperature annealing stepof carrying out a low temperature annealing operation at a temperatureof 150 to 450° C., after the finish cold rolling step. These steps willbe described below in detail. Furthermore, facing, pickling and so forthmay be optionally carried out after the hot rolling. After each heattreatment, pickling, polishing, degreasing and so forth may beoptionally carried out.

(Melting and Casting)

After the raw materials of a copper alloy are melted, an ingot isproduced by the continuous casting, semi-continuous casting or the like.Furthermore, in order to prevent oxidation of Ti, the raw materials arepreferably melted in an atmosphere of an inert gas or in a vacuummelting furnace. After casting, soaking (or hot forging) may beoptionally carried out.

(Hot Rolling)

The hot rolling for Cu—Ti alloys is usually carried out at a hightemperature of not lower than 700° C., preferably not lower than 750°C., so as to prevent deposits from being produced during rolling, andthen, quenching is carried out after the hot rolling is completed.However, on such typical hot rolling conditions, it is difficult toproduce a sheet material of a copper alloy having a uniform crystalgrain structure and a specific texture as a sheet material of a copperalloy according to the present invention. That is, on such typical hotrolling conditions, it is difficult to produce a sheet material of acopper alloy which has uniform crystal grains having a coefficient ofvariation of CV<0.45 and which has a principal orientation component of{420}, even if the conditions in the subsequent steps are widelychanged. For that reason, in the preferred embodiment of a method forproducing a sheet material of a copper alloy according to the presentinvention, the initial rolling pass is carried out in a temperaturerange of from 950° C. to 700° C., and hot rolling is carried out at arolling reduction of not less than 30% in a temperature range of fromless than 700° C. to 500° C.

When the hot rolling of the ingot is carried out, if the initial rollingpass is carried out in a high temperature range of not lower than 700°C. at which recrystallization is easy to occur, it is possible to breakthe cast structure to uniform components and structures. However, if thetemperature exceeds 950° C., it is required to set such a temperaturerange that cracks are not produced in portions, such as segregationportions of alloy components, at which the melting point is lowered.Therefore, in order to ensure the complete recrystallization during thehot rolling steps, the hot rolling operation is preferably carried outat a rolling reduction of not less than 60% in a temperature range offrom 950° C. to 700° C. Thus, the uniformity of the structure is furtherpromoted. Furthermore, since it is required to apply a great rollingload in order to obtain a rolling reduction of not less than 60% by onepass, the total rolling reduction of not less than 60% may be ensured bya plurality of passes. In the preferred embodiment of a method forproducing a sheet material of a copper alloy according to the presentinvention, the rolling reduction of not less than 30% is ensured in atemperature range of from not less than 700° C. to 500° C., at whichrolling strains are easily produced, at the hot rolling step. Thus, partof deposits are generated, and the cold rolling and solution treatmentat the subsequent steps are combined with the hot rolling, so that it iseasy to form a crystal grain structure having uniform crystal grainsizes and a recrystallized texture having a principal orientationcomponent of {420}. Furthermore, in this case, the hot rolling operationin a temperature range of from less than 700° C. to 500° C. may becarried by a plurality of passes. The rolling reduction in thistemperature range is preferably not less than 40%. The final passtemperature at the hot rolling step is preferably not higher than 600°C. The total rolling reduction at the hot rolling step may be about 80to 97%.

The rolling reduction ε (%) in a certain temperature range is calculatedby ε=(t₀−t₁)×100/t₀, assuming that the thickness of a plate before theinitial rolling pass of a plurality of rolling passes, which arecontinuously carried out in the temperature range, is t₀ (mm) and thatthe thickness of the plate after the final rolling pass of the pluralityof rolling passes is t₁ (mm). For example, the thickness of a platebefore the initial rolling pass is 120 mm, and a hot rolling operationis carried out in a temperature range of not lower than 700° C., so thatthe thickness of the plate after the final rolling pass at a temperatureof not lower than 700° C. is 30 mm. Then, the hot rolling operation issubsequently carried out, and the final pass of the hot rollingoperation is carried out in a temperature range of from less than 700°C. to 400° C., so that a plate of the copper alloy having a thickness of10 mm is finally obtained. In this case, the rolling reduction in thetemperature range of not less than 700° C. is (120−30)×100/120=75(%),and the rolling reduction in the temperature range of less than 700° C.to 400° C. is (30−10)×100/30=66.7(%), so that the total rollingreduction in the hot rolling operation is (120−10)×100/120=91.7(%).

(First Cold Rolling)

At the cold rolling step carried out before the solution treatment, therolling reduction is required to be not less than 85%, and preferablynot less than 90%. If the material worked at such a high rollingreduction is subjected to a solution treatment at the subsequent step,strains introduced at the high rolling reduction serve as nucleuses forrecrystallization. Thus, it is possible to obtain a crystal grainstructure having uniform crystal grain sizes, and it is possible to forma recrystallized texture having a principal orientation component of{420}. In particular, the recrystallized texture greatly depends on thecold-rolling reduction before recrystallization. Specifically, thecrystal orientation having a principal orientation component of {420} ishardly generated at a cold-rolling reduction of not higher than 60%, andis gradually increased at a cold-rolling reduction of 60 to 80% as thecold-rolling reduction is increased, the crystal orientation beingrapidly increased if the cold-rolling reduction exceeds about 85%. Inorder to obtain a crystal orientation wherein the orientation of {420}is sufficiently superior, the rolling reduction is required to be notless than 85%, and preferably not less than 90%. Furthermore, it is notparticularly required to define the upper limit of the cold-rollingreduction since it is necessarily limited by mill power and so forth.However, it is possible to obtain good results at a cold-rollingreduction of not higher than 99% in order to prevent cracks from beingproduced in edges.

Furthermore, in usual methods for producing a sheet material of a copperalloy, one or a plurality of cold rolling operations before and after anprocess annealing (intermediate solution treatment) are carried outbefore a solution treatment after a hot rolling operation. However, ifsuch cold rolling operations are carried out, the cold-rolling reductionimmediately before the solution treatment is lowered to increase thecoefficient of variation in grain size of crystal grain structure formedby the solution treatment, and the recrystallized texture having aprincipal orientation component of {420} is remarkably weaken.Therefore, such cold rolling operations are not carried out in thepreferred embodiment of a method for producing a sheet material of acopper alloy according to the present invention.

(Solution Treatment)

In usual methods for producing a sheet material of a copper alloy, thesolution treatment is carried out in order to form a solid solution ofsolute atoms into a matrix again and to carry out recrystallization. Inthe preferred embodiment of a method for producing a sheet material of acopper alloy according to the present invention, the solution treatmentis also carried out in order to form a recrystallized texture having aprincipal orientation component of {420}. It is required to carry outthe solution treatment at a higher temperature than the solid solubilitycurve of a copper alloy having a chemical composition (a solidsolubility curve defined by an equilibrium diagram) by 30° C. or more.If the temperature is too low, it is not possible to sufficiently formthe solid solution of beta phases. On the other hand, if the temperatureis too high, crystal grains are coarsened. In either case, it isdifficult to finally obtain a sheet material of a copper alloy having anexcellent bending workability and a high strength. For that reason, thesolution treatment is preferably carried out in a temperature rangewhich is higher than the solid solubility curve by 50 to 100° C.

In the solution treatment, a holding time in a heating furnace in atemperature range of from 750° C. to 1000° C. is preferably set to carryout a heat treatment so that the mean grain size of recrystallizedgrains (twin boundaries are not regarded as crystal grain boundaries) isin the range of from 5 μm to 25 μm, preferably in the range of from 8 μmto 20 μm. If the grain size of recrystallized grains is too small, therecrystallized texture having a principal orientation component of {420}is weak, and this is disadvantageous in order to improve the stressrelaxation resistance. On the other hand, if the grain size ofrecrystallized grains is too large, the surface of the bent portion ofthe sheet material of the copper alloy is easy to be rough. Furthermore,the grain size of recrystallized grains is varied by the cold-rollingreduction before the solution treatment and by chemical composition.However, if the relationship between the heat pattern in the solutiontreatment and the mean grain size is previously derived by experimentswith respect to the respective alloys, it is possible to set the holdingtime in the temperature range of from 750° C. to 1000° C. Specifically,in the chemical composition of a sheet material of a copper alloyaccording to the present invention, appropriate heating conditions canbe set on heating conditions for holding the plate at a temperature of750 to 1000° C. for 5 seconds to 5 minutes.

(Second Cold Rolling)

Then, a cold rolling operation is carried out at a rolling reduction of0 to 50%. The cold rolling at this stage has the function of promotingdeposition in the subsequent ageing treatment. Thus, it is possible tolower the ageing temperature for providing necessary characteristics,such as electric conductivity and hardness, or it is possible to shortenthe ageing time.

The texture having a principal orientation component of {220} isdeveloped by the cold rolling operation. However, crystal grains, whichhave the {420} plane parallel to the surface of the sheet material,sufficiently remain in the cold-rolling reduction of not higher than50%. The cold rolling operation at this stage is required to be carriedout at a rolling reduction of not higher than 50%, and is preferablycarried out at a rolling reduction of 0 to 40%. If the rolling reductionis too high, it is difficult to obtain an ideal crystal orientationsatisfying I{420}/I₀{420}>1.0. Furthermore, the rolling reduction of 0%means that the ageing treatment is directly carried out without carryingout the second cold rolling after the solution treatment. In thepreferred embodiment of a method for producing a sheet material of acopper alloy according to the present invention, the second cold rollingstep may be omitted in order to improve the productivity of the sheetmaterial of the copper alloy.

(Ageing Treatment)

At the ageing treatment step, the ageing temperature is set so as not tobe too high on effective conditions for improving the electricconductivity and strength of the sheet material of the copper alloy. Ifthe ageing temperature is too high, the crystal orientation having apreferred orientation of {420} developed by the solution treatment isweakened, so that there are some cases where it is not possible toobtain the function of sufficiently improving the bending workability ofthe sheet material of the copper alloy. Specifically, the ageingtemperature is preferably set so that the temperature of the sheetmaterial is in the range of from 300° C. to 550° C. The ageingtemperature is more preferably set so that the temperature of the sheetmaterial is in the range of from 350° C. to 500° C. The ageing time canbe set in the range of from about 60 minutes to about 600 minutes. Theageing treatment may be carried out in an atmosphere of hydrogen,nitrogen or argon in order to inhibit oxide films from being formed onthe surface of the sheet material during the ageing treatment.

In Cu—Ti alloys, stable phases (beta phases) are preferably inhibitedfrom being generated. For that reason, assuming that the ageingtemperature capable of obtaining the maximum hardness in the compositionof the Cu—Ti alloy is T_(M) (° C.) and that the maximum hardness thereofis H_(M) (HV), the ageing temperature at the ageing treatment step ispreferably set to be a temperature which ranges from 300° C. to 550° C.and which is T_(M)±10° C., and the ageing time is preferably set so thatthe hardness of the sheet material is in the range of from 0.90 H_(M) to0.95 H_(M). The ageing temperature T_(M) (° C.) capable of obtaining themaximum hardness, and the maximum hardness H_(M) (HV) can be previouslygrasped by pretests. In the composition range of a sheet material of acopper alloy according to the present invention, the hardness of thesheet material usually reaches the maximum hardness in an ageing time of24 hours or less.

Furthermore, if the requirement for the strength level is not so high(e.g., if the 0.2% yield strength is about 900 MPa), the finish coldrolling step and low temperature annealing step, which will be describedlater, may be omitted.

(Finish Cold Rolling)

The finish cold rolling has the function of highly improving thestrength level (particularly 0.2% yield strength) of the sheet materialof the copper alloy. If the finish cold-rolling reduction is too low,there is some possibility that a sufficient strength can not beobtained. However, as the rolling reduction is increased, the rollingtexture having a principal orientation component of {220} is developed.On the other hand, if the finish cold-rolling reduction is too high, therolling texture having a principal orientation component of {220} is toosuperior to other orientations, so that it is not possible to realize acrystal orientation having both of a high strength and an excellentbending workability in the bad way. In the preferred embodiment of amethod for producing a sheet material of a copper alloy according to thepresent invention, the finish cold-rolling reduction is preferably inthe range of from 0% to 30%, and more preferably in the range of 10% to20%. By this finish cold rolling, it is possible to maintain the crystalorientation satisfying I{420}/I₀{420}>1.0. Furthermore, the rollingreduction of 0% means that this cold rolling is not carried out.

The final thickness of the sheet material is preferably in the range offrom about 0.05 mm to about 0.1 mm, and more preferably in the range offrom 0.08 mm to 0.5 mm.

(Low Temperature Annealing)

After the finish cold rolling, the low temperature annealing may becarried out in order to reduce the residual stress of the sheet materialof the copper alloy, to improve the bending workability of the sheetmaterial, and to improve the stress relaxation resistance of the sheetmaterial due to the decrease of dislocation in vacancies and on the slipplane. In particular, Cu—Ti alloys are hardened by a low temperatureannealing in an appropriate temperature range. The heating temperaturein this low temperature annealing is preferably set so that thetemperature of the sheet material is in the range of from 150° C. to450° C. By this low temperature annealing, it is possible to improve allof the strength, electric conductivity, bending workability and stressrelaxation resistance of the sheet material of the copper alloy. If theheating temperature is too high, the sheet material of the copper alloyis softened in a short time, so that variations in characteristics areeasily caused in either of batch and continuous systems. On the otherhand, if the heating temperature is too low, it is not possible tosufficiently obtain the above-described functions of improving thecharacteristics. The holding time in the above-described temperaturerange is preferably not less than 5 seconds, and good results can beusually obtained when the holding time is not longer than 1 hour.

The examples of sheet materials of copper alloys and methods forproducing the same according to the present invention will be describedbelow in detail.

Examples 1-12

There were melted a copper alloy containing 3.18 wt % of Ti and thebalance being Cu (Example 1), a copper alloy containing 4.08 wt % of Tiand the balance being Cu (Example 2), a copper alloy containing 3.58 wt% of Ti and the balance being Cu (Example 3), a copper alloy containing4.64 wt % of Ti and the balance being Cu (Example 4), a copper alloycontaining 2.86 wt % of Ti, 0.12 wt % of Co, 0.22 wt % of Ni and thebalance being Cu (Example 5), 2.32 wt % of Ti, 0.14 wt % of Fe, 0.11 wt% of Sn, 0.36 wt % of Zn and the balance being Cu (Example 6), a copperalloy containing 1.93 wt % of Ti, 0.54 wt % of Ni, 0.08 wt % of Sn, 0.10wt % of Mg, 0.11 wt % of Zr and the balance being Cu (Example 7), acopper alloy containing 1.55 wt % of Ti, 0.12 wt % of Ni, 0.21 wt % ofCr, 0.03 wt % of B and the balance being Cu (Example 8), a copper alloycontaining 3.20 wt % of Ti, 0.14 wt % of Al, 0.03 wt % of P and thebalance being Cu (Example 9), a copper alloy containing 3.06 wt % of Ti,0.12 wt % of V, 0.06 wt % of Mn and the balance being Cu (Example 10), acopper alloy containing 3.14 wt % of Ti, 0.12 wt % of Ag, 0.06 wt % ofBe and the balance being Cu (Example 11), and a copper alloy containing3.35 wt % of Ti, 0.24 wt % of misch metal and the balance being Cu(Example 12), respectively. Then, a vertical semi-continuous castingmachine was used for casting the melted copper alloys to obtain ingotshaving a thickness of 60 mm, respectively.

Each of the ingots was heated to 950° C., and then, extracted to starthot rolling. The pass schedule in the hot rolling was set so that therolling reduction in a temperature range of not lower than 750° C. wasnot less than 60% while rolling was carried out even in a temperaturerange of lower than 700° C. Furthermore, the hot-rolling reductions inthe temperature range of from less than 700° C. to 500° C. were 42%(Example 1), 35% (Example 2), 32% (Example 3), 30% (Example 4), 50%(Example 5), 57% (Example 6), 50% (Example 7), 55% (Example 8), 45%(Example 9), 40% (Example 10), 40% (Example 11) and 40% (Example 12),respectively, and the final pass temperature in the hot rolling was atemperature of 600 to 500° C. The total hot-rolling reduction from theingot was about 95%. After the hot rolling, the surface oxide layer wasremoved (faced) by mechanical polishing.

Then, cold rolling was carried out at rolling reductions of 98% (Example1), 92% (Example 2), 95% (Example 3), 90% (Example 4), 90% (Example 5),96% (Example 6), 98% (Example 7), 96% (Example 8), 96% (Example 9), 95%(Example 10), 86% (Example 11) and 92% (Example 12) to form plates ofthe copper alloys, respectively, and then, a solution treatment wascarried out. In this solution treatment, a heat treatment was carriedout at a heating temperature, which was set to be a higher temperaturethan the solid solubility curve of the composition of each alloy by 30°C. or more in a temperature range of from 750° C. to 1000° C., for aholding time, which was set to be in the range of from 5 seconds to 5minutes, so that the mean crystal grain size after the solutiontreatment in each example (twin boundaries were not regarded as crystalgrain boundaries) was in the range of from 5 μm to 25 μm. Specifically,the heat treatment was carried out at 900° C. for 15 seconds (Example1), at 950° C. for 15 seconds (Example 2), at 900° C. for 25 seconds(Example 3), at 1000° C. for 15 seconds (Example 4), at 850° C. for 20seconds (Example 5), at 850° C. for 15 seconds (Example 6), at 830° C.for 15 seconds (Example 7), at 850° C. for seconds (Example 8), at 900°C. for 18 seconds (Example 9), at 900° C. for 20 seconds (Example 10),at 900° C. for 25 seconds (Example 11) and at 900° C. for 20 seconds(Example 12), respectively.

Then, the plates after the solution treatment were cold-rolled atrolling reductions of 15% (Example 1), 20% (Example 2), 0% (Example 3),25% (Example 4), 15% (Example 5), 45% (Example 6), 20% (Example 7), 20%(Example 8), 15% (Example 9), 0% (Example 10), 0% (Example 11) and 0%(Example 12), respectively.

With respect to the plates thus obtained, ageing treatment experimentsup to 24 hours were carried out in a temperature range of from 300° C.to 500° C. as pretests to grasp ageing conditions (ageing temperatureT_(M) (° C.), ageing time t_(M) (min), maximum hardness H_(M) (HV)) onwhich the maximum hardness was obtained in accordance with thecompositions of the alloys. Then, the ageing temperature was set to bein the range of T_(M)±10° C., and the ageing time was set to be a periodof time which was shorter than t_(M) and which causes the hardness ofthe plate after ageing to be in the range of from 0.90 H_(M) to 0.95H_(M).

Then, the plates after the ageing treatment were finish cold-rolled atrolling reductions of 10% (Example 1), 0% (Example 2), 12% (Example 3),0% (Example 4), 15% (Example 5), 0% (Example 6), 25% (Example 7), 30%(Example 8), 15% (Example 9), 25% (Example 10), 10% (Example 11) and 15%(Example 12), respectively. Then, a low temperature annealing forholding each plate in an annealing furnace at 450° C. for one minute wascarried out.

The sheet materials of the copper alloys were thus obtained in Examples1-12. Furthermore, facing was optionally carried out in the middle ofthe production of the sheet materials so that the thickness of eachsheet material was 0.15 mm.

Then, samples were cut out from the sheet materials of copper alloysobtained in these examples, to derive the mean crystal grain size ofcrystal grain structure, (maximum crystal grain size−minimum crystalgrain size)/(mean crystal grain size), intensity of X-ray diffraction,electric conductivity, tensile strength, 0.2% yield strength, usualbending workability, bending workability after notching, stressrelaxation resistance of each sheet material as follows.

The mean crystal grain size of crystal grain structure was calculated asfollows. First, the surface (rolled surface) of the sheet material ofthe copper alloy was polished and etched. Then, from the opticalmicrophotograph of the rolled surface of the sheet material of thecopper alloy, ten square visual fields having a size of 100 μm×100 μmwere selected at random, two sides of each of the visual fields beingparallel to the rolling direction (LD) and the other two sides of eachof the visual fields being parallel to a direction (TD) perpendicular tothe rolling direction. In each of the visual fields, crystal grain sizeswere measured by the method of section based on JIS H0501. Then, themean values d₁, d₂, . . . , d₁₀ of the crystal grain sizes in each ofthe visual fields were calculated, respectively. Then, the mean valued_(mean) (=(d₁+d₂+ . . . +d₁₀)/10) of the mean values d₁, d₂, . . . ,d₁₀ of the crystal grain sizes was calculated as the mean crystal grainsize of crystal grain structure. Furthermore, crystal grains extend inthe rolling direction by rolling after the solution treatment. However,after the sheet material is rolled after the solution treatment, thelength of crystal grains in the direction (TD) perpendicular to therolling direction is substantially equal to the length of crystal grainsin the TD after the solution treatment. Therefore, the measurement ofcrystal grain sizes was carried out by measuring the length of crystalgrains in the direction (TD) perpendicular to the rolling direction. Asa result, the mean crystal grain sizes were 8 μm (Example 1), 12 μm(Example 2), 16 μm (Example 3), 6 μm (Example 4), 18 μm (Example 5), 15μm (Example 6), 10 μm (Example 7), 14 μm (Example 8), 11 μm (Example 9),12 μm (Example 10), 16 μm (Example 11) and 12 μm (Example 12),respectively.

In addition, (maximum crystal grain size−minimum crystal grainsize)/(mean crystal grain size) was calculated as(d_(max)−d_(min))/d_(mean), assuming that the maximum value of the meanvalues d₁, d₂, . . . , d₁₀ of crystal grain sizes in each of the visualfields was the maximum crystal grain size d_(max) and that the minimumvalue thereof was the minimum crystal grain size d_(min). As a result,the values of (maximum crystal grain size−minimum crystal grainsize)/(mean crystal grain size) were 0.06 (Example 1), 0.08 (Example 2),0.09 (Example 3), 0.12 (Example 4), 0.08 (Example 5), 0.05 (Example 6),0.07 (Example 7), 0.10 (Example 8), 0.14 (Example 9), 0.11 (Example 10),0.09 (Example 11) and 0.06 (Example 12), respectively.

The measurement of the intensity of X-ray diffraction (the integratedintensity of X-ray diffraction) was carried out as follows. First,samples were prepared by finish polishing the surface (rolled surface)of the sheet material of the copper alloy with a #1500 waterproof paper.Then, with respect to the finished surface of each sample, the intensityI{420} of X-ray diffraction on the {420} plane and the intensity I{220}of X-ray diffraction on the {220} plane were measured by means of anX-ray diffractometer (XRD) on the measuring conditions which containMo-Kα rays, an X-ray tube voltage of 40 kV and an X-ray tube current of30 mA. On the other hand, with respect to the standard powder of purecopper, the intensity I₀{420} of X-ray diffraction on the {420} planeand the intensity I₀{220} on the {220} plane were also measured by meansof the same X-ray diffractometer on the same measuring conditions. Usingthese measured values, the ratio I{420}/I₀{420} of the intensities ofX-ray diffraction, and the ratio I{220}/I₀{220} of the intensities ofX-ray diffraction were derived. As a result, I{420}/I₀{420} andI{220}/I₀{220} were 1.3 and 2.8 (Example 1), 1.6 and 2.6 (Example 2),1.5 and 2.7 (Example 3), 2.0 and 2.6 (Example 4), 1.4 and 3.2 (Example5), 2.0 and 2.6 (Example 6), 1.5 and 2.8 (Example 7), 1.4 and 2.6(Example 8), 1.2 and 3.2 (Example 9), 1.1 and 3.6 (Example 10), 1.6 and2.5 (Example 11), and 1.4 and 2.7 (Example 12), respectively.

The electric conductivity of the sheet material of the copper alloy wasmeasured in accordance with the electric conductivity measuring methodbased on JIS H0505. As a result, the electric conductivities were 13.2%IACS (Example 1), 12.2% IACS (Example 2), 12.4% IACS (Example 3), 13.0%IACS (Example 4), 13.6% IACS (Example 5), 14.5% IACS (Example 6), 15.1%IACS (Example 7), 16.2% IACS (Example 8), 12.4% IACS (Example 9), 12.6%IACS (Example 10), 13.1% IACS (Example 11) and 12.8% IACS (Example 12),respectively.

In order to evaluate the tensile strength serving as one of mechanicalcharacteristics of the sheet material of the copper alloy, three testpieces (No. 5 test pieces based on JIS Z2201) for tension test in the LD(rolling direction) were cut out from each of the sheet materials ofcopper alloys. Then, the tension test based on JIS Z2241 was carried outwith respect to each of the test pieces to derive the mean value oftensile strengths in the LD and the mean value of 0.2% yield strengths.As a result, the tensile strength in the LD and the 0.2% yield strengthwere 1005 MPa and 935 MPa (Example 1), 1016 MPa and 915 MPa (Example 2),976 MPa and 905 MPa (Example 3), 1025 MPa and 946 MPa (Example 4), 980MPa and 912 MPa (Example 5), 986 MPa and 888 MPa (Example 6), 968 MPaand 892 MPa (Example 7), 976 MPa and 965 MPa (Example 8), 1025 MPa and955 MPa (Example 9), 1036 MPa and 970 MPa (Example 10), 1025 MPa and 955MPa (Example 11), and 1034 MPa and 967 MPa (Example 12), respectively.

In order to evaluate the stress relaxation resistance of the sheetmaterial of the copper alloy, a bending test piece (width: 10 mm) havinga longitudinal direction of TD (the direction perpendicular to therolling direction and thickness direction) was cut out from the sheetmaterial of the copper alloy. Then, the bending test piece was bent inthe form of an arch so that the surface stress in the central portion ofthe test piece in the longitudinal direction thereof is 80% of the 0.2%yield strength, and then, the test piece was fixed in this state.Furthermore, the surface stress is defined by surface stress (MPa)=6Etδ/L₀ ² wherein E denotes the modulus of elasticity (MPa), and t denotesthe thickness (mm) of the sample, δ denoting the deflection height (mm)of the sample. From the bending deformation after the test piece in thisstate was held at 200° C. for 1000 hours in the atmosphere, the stressrelaxation rate was calculated by stress relaxation rate(%)=(L₁−L₂)×100/(L₁−L₀) wherein L₀ denotes the length of a jig, i.e.,the horizontal distance (mm) between both ends of the fixed sampleduring the test, and L₁ denotes the length (mm) of the sample when thetest starts, L₂ denoting the horizontal distance (mm) between both endsof the sample after the test. As a result, the stress relaxation rateswere 2.4% (Example 1), 2.2% (Example 2), 2.8% (Example 3), 3.1% (Example4), 2.2% (Example 5), 3.4% (Example 6), 3.3% (Example 7), 3.4% (Example8), 3.6% (Example 9), 3.3% (Example 10), 2.2% (Example 11) and 2.3%(Example 12), respectively. Furthermore, it was evaluated that the sheetmaterial of the copper alloy having a stress relaxation rate of nothigher than 5% has a high durability even if the sheet material is usedas the material of connectors for automobiles, and it was judged thatsuch a sheet material of the copper alloy was acceptable.

In order to evaluate the usual bending workability of the sheet materialof the copper alloy, three bending test pieces (width: 10 mm) having alongitudinal direction of LD (rolling direction), and three bending testpieces (width: 10 mm) having a longitudinal direction of TD (thedirection perpendicular to the rolling direction and thicknessdirection) were cut out from the sheet material of the copper alloy,respectively. Then, the 90° W bending test based on JIS H3110 wascarried out with respect to each of the test pieces. Then, the surfaceand section of the bent portion of each test piece after the test wereobserved at a magnification of 100 by means of an optical microscope, toderive a minimum bending radius R at which cracks are not produced.Then, the minimum bending radius R was divided by the thickness t of thesheet material of the copper alloy, to derive the values of R/t in theLD and TD, respectively. The worst result of the values of R/t withrespect to the three test pieces in each of the LD and TD was adopted asthe value of R/t in the LD and TD, respectively. As a result, the valuesof R/t in the LD and TD were 0.0 and 0.5 (Examples 1, 4 and 11), 0.0 and0.0 (Examples 2, 3, 6, 7 and 8), 0.0 and 0.3 (Example 5), 0.0 and 0.7(Example 9 and 12), and 0.0 and 0.8 (Example 10), respectively.

In order to evaluate the bending workability after notching of the sheetmaterial of the copper alloy, a strip sample (width: 10 mm) having alongitudinal direction of LD was cut out from the sheet material of thecopper alloy. Then, a notch extending over the whole width of a sample12 was formed by applying a load of 20 kN to the sample 12 in thedirection of arrow A as shown in FIG. 3, using a notch forming jig 10wherein a protruding portion having a substantially trapezoid section isformed on the top surface thereof (the width of the flat top surface ofthe protruding portion is 0.1 mm, and the angle between each side of theprotruding portion and the flat surface is 45°) as shown in FIGS. 2 and3. Furthermore, the longitudinal direction of the notch (i.e., thedirection parallel to the groove) was a direction perpendicular to thelongitudinal direction (the direction of arrow B) of the sample. Thedepth of the notch 12′a of each of three notched bending test pieces 12′thus prepared was measured. The depth δ of the notch 12′a schematicallyshown in FIG. 4 was about ¼ to about ⅙ as much as the thickness t of thesample. With respect to each of the three notched bending test pieces12′, the 90° W bending test based on JIS H3110 was carried out. The 90°W bending test was carried out by means of a jig wherein R of the tip ofthe central protruding portion of the lower die was 0 mm. In this 90° Wbending test, the notched bending test piece 12′ was so set that thenotch forming surface faces downward while the central protrudingportion of the lower die corresponds to the notch portion. Then, thesurface and section of the bent portion of each of the three test piecesafter the test were observed at a magnification of 100 by means of anoptical microscope, to determine the presence of cracks. The worstresult of the test pieces was adopted to evaluate the bendingworkability of the bent portion after notching. As a result, in all ofthe examples, cracks are not observed on the surface and section of thebent portion after notching, so that the bending workability afternotching was good.

Comparative Example 1

A copper alloy having the same composition as that in Example 1 was usedfor obtaining a sheet material of the copper alloy by the same method asthat in Example 1, except that the hot-rolling reduction in thetemperature range of less than 700° C. to 500° C. was 20% and that aplurality of cold rolling operations before and after the processannealing (intermediate solution treatment) at 850° C. for 120 secondswere carried out during the cold rolling before the solution treatment.Furthermore, a heat treatment was carried out at 800° C. for 150 secondsin the solution treatment.

Samples were cut out from the sheet material of the copper alloy thusobtained, to derive the mean crystal grain size of crystal grainstructure, (maximum crystal grain size−minimum crystal grain size)/(meancrystal grain size), intensity of X-ray diffraction, electricconductivity, tensile strength, 0.2% yield strength, usual bendingworkability, bending workability after notching, and stress relaxationresistance thereof by the same methods as those in Examples 1-12.

As a result, the mean crystal grain size was 5 μm, and (maximum crystalgrain size−minimum crystal grain size)/(mean crystal grain size) was0.42. The ratios I{420}/I₀{420} and I{220}/I₀{220} of the intensities ofX-ray diffraction were 0.6 and 4.4, respectively. The electricconductivity was 13.3% IACS. The tensile strength in the LD and the 0.2%yield strength were MPa and 928 MPa, respectively. The stress relaxationrate was 4.2%. As the evaluation of the usual bending workability, thevalues of R/t in the LD and TD were 2.0 and 3.0, respectively. Thesample was broken at the bent portion after notching.

Comparative Example 2

A copper alloy having the same composition as that in Example 2 was usedfor obtaining a sheet material of the copper alloy by the same method asthat in Example 2, except that the hot-rolling reduction in thetemperature range of less than 700° C. to 500° C. was 25% and that aplurality of cold rolling operations before and after the processannealing (intermediate solution treatment) at 850° C. for 120 secondswere carried out during the cold rolling before the solution treatment.Furthermore, a heat treatment was carried out at 950° C. for 15 secondsin the solution treatment.

Samples were cut out from the sheet material of the copper alloy thusobtained, to derive the mean crystal grain size of crystal grainstructure, (maximum crystal grain size−minimum crystal grain size)/(meancrystal grain size), intensity of X-ray diffraction, electricconductivity, tensile strength, 0.2% yield strength, usual bendingworkability, bending workability after notching, and stress relaxationresistance thereof by the same methods as those in Examples 1-12.

As a result, the mean crystal grain size was 12 μm, and (maximum crystalgrain size−minimum crystal grain size)/(mean crystal grain size) was0.36. The ratios I{420}/I₀{420} and I{220}/I₀{220} of the intensities ofX-ray diffraction were 0.4 and 3.2, respectively. The electricconductivity was 12.6% IACS. The tensile strength in the LD and the 0.2%yield strength were 996 MPa and 906 MPa, respectively. The stressrelaxation rate was 3.9%. As the evaluation of the usual bendingworkability, the values of R/t in the LD and TD were 1.0 and 2.5,respectively. The sample was broken at the bent portion after notching.

Comparative Example 3

A copper alloy having the same composition as that in Example 3 was usedfor obtaining a sheet material of the copper alloy by the same method asthat in Example 3, except that the hot-rolling reduction in thetemperature range of less than 700° C. to 500° C. was 0%, i.e., thehot-rolling completing temperature was not lower than 700° C., and thata plurality of cold rolling operations before and after the processannealing (intermediate solution treatment) at 850° C. for 120 secondswere carried out during the cold rolling before the solution treatment.Furthermore, a heat treatment was carried out at 850° C. for 120 secondsin the solution treatment.

Samples were cut out from the sheet material of the copper alloy thusobtained, to derive the mean crystal grain size of crystal grainstructure, (maximum crystal grain size−minimum crystal grain size)/(meancrystal grain size), intensity of X-ray diffraction, electricconductivity, tensile strength, 0.2% yield strength, usual bendingworkability, bending workability after notching, and stress relaxationresistance thereof by the same methods as those in Examples 1-12.

As a result, the mean crystal grain size was 18 μm, and (maximum crystalgrain size−minimum crystal grain size)/(mean crystal grain size) was0.35. The ratios I{420}/I₀{420} and I{220}/I₀{220} of the intensities ofX-ray diffraction were 0.3 and 4.1, respectively. The electricconductivity was 12.7% IACS. The tensile strength in the LD and the 0.2%yield strength were 963 MPa and 898 MPa, respectively. The stressrelaxation rate was 4.2%. As the evaluation of the usual bendingworkability, the values of R/t in the LD and TD were 1.5 and 2.5,respectively. Cracks were observed on the surface and section of thebent portion after notching.

Comparative Example 4

A copper alloy having the same composition as that in Example 4 was usedfor obtaining a sheet material of the copper alloy by the same method asthat in Example 4, except that the hot-rolling reduction in thetemperature range of less than 700° C. to 500° C. was 0%, i.e., thehot-rolling completing temperature was not lower than 700° C., and thata plurality of cold rolling operations before and after the processannealing (intermediate solution treatment) at 850° C. for 120 secondswere carried out during the cold rolling before the solution treatment.Furthermore, a heat treatment was carried out at 950° C. for 15 secondsin the solution treatment.

Samples were cut out from the sheet material of the copper alloy thusobtained, to derive the mean crystal grain size of crystal grainstructure, (maximum crystal grain size−minimum crystal grain size)/(meancrystal grain size), intensity of X-ray diffraction, electricconductivity, tensile strength, 0.2% yield strength, usual bendingworkability, bending workability after notching, and stress relaxationresistance thereof by the same methods as those in Examples 1-12.

As a result, the mean crystal grain size was 5 μm, and (maximum crystalgrain size−minimum crystal grain size)/(mean crystal grain size) was0.33. The ratios I{420}/I₀{420} and I{220}/I₀{220} of the intensities ofX-ray diffraction were 0.7 and 3.8, respectively. The electricconductivity was 13.1% IACS. The tensile strength in the LD and the 0.2%yield strength were 1011 MPa and 952 MPa, respectively. The stressrelaxation rate was 5.4%. As the evaluation of the usual bendingworkability, the values of R/t in the LD and TD were 2.0 and 3.5,respectively. Cracks were observed on the surface and section of thebent portion after notching.

Comparative Example 5

A copper alloy having the same composition as that in Example 5 was usedfor obtaining a sheet material of the copper alloy by the same method asthat in Example 5, except that the hot-rolling reduction in thetemperature range of less than 700° C. to 500° C. was 15%, that aplurality of cold rolling operations before and after the processannealing (intermediate solution treatment) at 850° C. for 120 secondswere carried out during the cold rolling before the solution treatment,and that the ageing time was so set that the hardness of the sheetmaterial after ageing be 1.00 with respect to the maximum hardness afterageing. Furthermore, a heat treatment was carried out at 850° C. for 15seconds in the solution treatment.

Samples were cut out from the sheet material of the copper alloy thusobtained, to derive the mean crystal grain size of crystal grainstructure, (maximum crystal grain size−minimum crystal grain size)/(meancrystal grain size), intensity of X-ray diffraction, electricconductivity, tensile strength, 0.2% yield strength, usual bendingworkability, bending workability after notching, and stress relaxationresistance thereof by the same methods as those in Examples 1-12.

As a result, the mean crystal grain size was 3 μm, and (maximum crystalgrain size−minimum crystal grain size)/(mean crystal grain size) was0.28. The ratios I{420}/I₀{420} and I{220}/I₀{220} of the intensities ofX-ray diffraction were 0.3 and 4.3, respectively. The electricconductivity was 14.1% IACS. The tensile strength in the LD and the 0.2%yield strength were 986 MPa and 908 MPa, respectively. The stressrelaxation rate was 7.6%. As the evaluation of the usual bendingworkability, the values of R/t in the LD and TD were 2.0 and 5.0,respectively. The sample was broken at the bent portion after notching.

Comparative Example 6

A sheet material of a copper alloy was obtained by the same method asthat in Examples 1-12, except that a copper alloy containing 1.08 wt %of Ti, 0.17 wt % of Mg, 0.20 wt % of Zr and the balance being Cu wasused as the melted copper alloy, that the hot-rolling reduction in thetemperature range of less than 700° C. to 500° C. was 45%, that thecold-rolling reduction before the solution treatment was 96%, that thecold-rolling reduction after the solution treatment was 50%, and thatthe finish cold-rolling reduction was 20%. Furthermore, a heat treatmentwas carried out at 750° C. for 20 seconds in the solution treatment.

Samples were cut out from the sheet material of the copper alloy thusobtained, to derive the mean crystal grain size of crystal grainstructure, (maximum crystal grain size−minimum crystal grain size)/(meancrystal grain size), intensity of X-ray diffraction, electricconductivity, tensile strength, 0.2% yield strength, usual bendingworkability, bending workability after notching, and stress relaxationresistance thereof by the same methods as those in Examples 1-12.

As a result, the mean crystal grain size was 8 μm, and (maximum crystalgrain size−minimum crystal grain size)/(mean crystal grain size) was0.35. The ratios 1{420}/I₀{420} and I{220}/I₀{220} of the intensities ofX-ray diffraction were 0.3 and 4.3, respectively. The electricconductivity was 22.5% IACS. The tensile strength in the LD and the 0.2%yield strength were 842 MPa and 768 MPa, respectively. The stressrelaxation rate was 6.4%. As the evaluation of the usual bendingworkability, the values of R/t in the LD and TD were 1.0 and 2.5,respectively. Cracks were observed on the surface and section of thebent portion after notching.

Comparative Example 7

A sheet material of a copper alloy was obtained by the same method asthat in Example 1, except that a copper alloy containing 5.22 wt % ofTi, 0.15 wt % of Ni, 0.15 wt % of Zn and the balance being Cu was usedas the melted copper alloy. Since the content of Ti was too high in thiscomparative example to set appropriate solution treatment conditions,cracks were produced during production, so that it was not possible toproduce any sheet material to be evaluated.

Comparative Example 8

A copper alloy having the same composition as that in Example 1 was usedfor obtaining a sheet material of the copper alloy by the same method asthat in Example 1, except that the solution treatment time was a longerperiod of time of 10 minutes. Furthermore, a heat treatment was carriedout at 900° C. in the solution treatment.

Samples were cut out from the sheet material of the copper alloy thusobtained, to derive the mean crystal grain size of crystal grainstructure, (maximum crystal grain size−minimum crystal grain size)/(meancrystal grain size), intensity of X-ray diffraction, electricconductivity, tensile strength, 0.2% yield strength, usual bendingworkability, bending workability after notching, and stress relaxationresistance thereof by the same methods as those in Examples 1-12.

As a result, the mean crystal grain size was 62 μm, and (maximum crystalgrain size−minimum crystal grain size)/(mean crystal grain size) was0.06. The ratios I{420}/I₀{420} and I{220}/I₀{220} of the intensities ofX-ray diffraction were 1.8 and 2.4, respectively. The electricconductivity was 12.7% IACS. The tensile strength in the LD and the 0.2%yield strength were 928 MPa and 856 MPa, respectively. The stressrelaxation rate was 2.0%. As the evaluation of the usual bendingworkability, the values of R/t in the LD and TD were 2.0 and 2.5,respectively. Cracks were observed on the surface and section of thebent portion after notching.

Comparative Example 9

A copper alloy having the same composition as that in Example 1 was usedfor obtaining a sheet material of the copper alloy by the same method asthat in Example 1, except that the solution treatment temperature was alower temperature of 700° C. and that the solution treatment time was alonger period of time of 10 minutes.

Samples were cut out from the sheet material of the copper alloy thusobtained, to derive the mean crystal grain size of crystal grainstructure, (maximum crystal grain size−minimum crystal grain size)/(meancrystal grain size), intensity of X-ray diffraction, electricconductivity, tensile strength, 0.2% yield strength, usual bendingworkability, bending workability after notching, and stress relaxationresistance thereof by the same methods as those in Examples 1-12.

As a result, the mean crystal grain size was 3 μm, and (maximum crystalgrain size−minimum crystal grain size)/(mean crystal grain size) was0.48. The ratios I{420}/I₀{420} and I{220}/I₀{220} of the intensities ofX-ray diffraction were 0.2 and 6.1, respectively. The electricconductivity was 15.6% IACS. The tensile strength in the LD and the 0.2%yield strength were 1026 MPa and 945 MPa, respectively. The stressrelaxation rate was 11.6%. As the evaluation of the usual bendingworkability, the value of R/t in the LD was 3.0, and the sample wasbroken even if the value of R/t in the TD was 5.0. The sample was brokenat the bent portion after notching.

Comparative Example 10

A copper alloy having the same composition as that in Example 1 was usedfor obtaining a sheet material of the copper alloy by the same method asthat in Example 1, except that the finish cold-rolling reduction was55%. Furthermore, a heat treatment was carried out at 900° C. for 15seconds in the solution treatment.

Samples were cut out from the sheet material of the copper alloy thusobtained, to derive the mean crystal grain size of crystal grainstructure, (maximum crystal grain size−minimum crystal grain size)/(meancrystal grain size), intensity of X-ray diffraction, electricconductivity, tensile strength, 0.2% yield strength, usual bendingworkability, bending workability after notching, and stress relaxationresistance thereof by the same methods as those in Examples 1-12.

As a result, the mean crystal grain size was 8 μm, and (maximum crystalgrain size−minimum crystal grain size)/(mean crystal grain size) was0.06. The ratios I{420}/I₀{420} and I{220}/I₀{220} of the intensities ofX-ray diffraction were 0.2 and 5.6, respectively. The electricconductivity was 12.4% IACS. The tensile strength in the LD and the 0.2%yield strength were 1114 MPa and 1056 MPa, respectively. The stressrelaxation rate was 6.4%. As the evaluation of the usual bendingworkability, the sample was broken even if the value of R/t in each ofthe LD and TD was 5.0. The sample was broken at the bent portion afternotching.

Comparative Example 11

A sheet material of a commercially-available typical Cu—Tialloy(C199-1/2H, thickness: 0.15 mm) was prepared. Samples were cut outfrom the prepared sheet material of the copper alloy, to derive the meancrystal grain size of crystal grain structure, (maximum crystal grainsize−minimum crystal grain size)/(mean crystal grain size), intensity ofX-ray diffraction, electric conductivity, tensile strength, 0.2% yieldstrength, usual bending workability, bending workability after notching,and stress relaxation resistance thereof by the same methods as those inExamples 1-12.

As a result, the mean crystal grain size was 7 μm, and (maximum crystalgrain size−minimum crystal grain size)/(mean crystal grain size) was0.25. The ratios I{420}/I₀{420} and I{220}/I₀{220} of the intensities ofX-ray diffraction were 0.5 and 3.3, respectively. The electricconductivity was 13.1% IACS. The tensile strength in the LD and the 0.2%yield strength were 854 MPa and 766 MPa, respectively. The stressrelaxation rate was 5.8%. As the evaluation of the usual bendingworkability, the values of R/t in the LD and TD were 1.5 and 2.0,respectively. Cracks were observed on the surface and section of thebent portion after notching.

Comparative Example 12

A sheet material of a commercially-available typical Cu—Ti alloy(C199-EH, thickness: 0.15 mm) was prepared. Samples were cut out fromthe prepared sheet material of the copper alloy, to derive the meancrystal grain size of crystal grain structure, (maximum crystal grainsize−minimum crystal grain size)/(mean crystal grain size), intensity ofX-ray diffraction, electric conductivity, tensile strength, 0.2% yieldstrength, usual bending workability, bending workability after notching,and stress relaxation resistance thereof by the same methods as those inExamples 1-12.

As a result, the mean crystal grain size was 7 μm, and (maximum crystalgrain size−minimum crystal grain size)/(mean crystal grain size) was0.28. The ratios I{420}/I₀{420} and I{220}/I₀{220} of the intensities ofX-ray diffraction were 0.3 and 3.9, respectively. The electricconductivity was 12.4% IACS. The tensile strength in the LD and the 0.2%yield strength were 962 MPa and 902 MPa, respectively. The stressrelaxation rate was 6.2%. As the evaluation of the usual bendingworkability, the values of R/t in the LD and TD were 2.0 and 4.0,respectively. The sample was broken at the bent portion after notching.

The compositions and producing conditions in the examples andcomparative examples are shown in Tables 1 and 2, respectively, and theresults with respect to structures and characteristics therein are shownin Tables 3 and 4, respectively.

TABLE 1 Chemical Composition (wt %) Cu Ti Fe Co Ni others Ex. 1 bal.3.18 — — — — Ex. 2 bal. 4.08 — — — — Ex. 3 bal. 3.58 — — — — Ex. 4 bal.4.64 — — — — Ex. 5 bal. 2.86 — 0.12 0.22 — Ex. 6 bal. 2.32 0.14 — — Sn:0.11, Zn: 0.36 Ex. 7 bal. 1.93 — — 0.54 Sn: 0.08, Mg: 0.10, Zr: 0.11 Ex.8 bal. 1.55 — — 0.12 Cr: 0.21, B: 0.03 Ex. 9 bal. 3.20 — — — Al: 0.14,P: 0.03 Ex. 10 bal. 3.06 — — — V: 0.12, Mn: 0.06 Ex. 11 bal. 3.14 — — —Ag: 0.12, Be: 0.06 Ex. 12 bal. 3.35 — — — misch metal: 0.24 Comp. 1 bal.3.18 — — — — Comp. 2 bal. 4.08 — — — — Comp. 3 bal. 3.58 — — — — Comp. 4bal. 4.64 — — — — Comp. 5 bal. 2.86 — 0.12 0.22 — Comp. 6 bal. 1.08 — —— Mg: 0.17, Zr: 0.20 Comp. 7 bal. 5.22 — — 0.15 Zn: 0.15 Comp. 8 bal.3.18 — — — — Comp. 9 bal. 3.18 — — — — Comp. 10 bal. 3.18 — — — — Comp.11 bal. 3.22 — — — — Comp. 12 bal. 3.16 — — — —

TABLE 2 Manufacturing Conditions Hot-rolling Ageing Reduction (%)Cold-rolling Solution Treatment Conditions in temperatures Reduction (%)Conditions Hardness after ranging from Before After Furnace Holdingageing/Maximum Finish less than 700° C. Solution Solution TemperatureTime Hardness after Cold-rolling to 500° C. Treatment Treatment (° C.)(sec) ageing Reduction (%) Ex. 1 42 98 15 900 15 0.93 10 Ex. 2 35 92 20950 15 0.92 0 Ex. 3 32 95 0 900 25 0.94 12 Ex. 4 30 90 25 1000  15 0.930 Ex. 5 50 90 15 850 20 0.94 15 Ex. 6 57 96 45 850 15 0.95 0 Ex. 7 50 9820 830 15 0.95 25 Ex. 8 55 96 20 850 8 0.94 30 Ex. 9 45 96 15 900 180.94 15 Ex. 10 40 95 0 900 20 0.94 25 Ex. 11 40 86 0 900 25 0.94 10 Ex.12 40 92 0 900 20 0.94 15 Comp. 1 20 98 15 800 150 0.93 10 Comp. 2 25 9220 950 15 0.92 0 Comp. 3 0 95 0 850 120 0.94 12 Comp. 4 0 90 25 950 150.93 0 Comp. 5 15 90 15 850 15 1.00 15 Comp. 6 45 96 50 750 20 0.95 20Comp. 7 — — — — — — — Comp. 8 42 98 15 900 600 0.93 10 Comp. 9 42 98 15700 600 0.93 10 Comp. 10 42 98 15 900 15 0.93 55 Comp. 11 — — — — — — —Comp. 12 — — — — — — —

TABLE 3 Structure Mean (Maximum Crystal Grain Ratio of IntensitiesCrystal Size − Minimum Crystal of X-ray Diffraction Grain Size GrainSize)/Mean I{420}/ I{220}/ (μm) Crystal Grain Size Io{420} Io{220} Ex. 18 0.06 1.3 2.8 Ex. 2 12 0.08 1.6 2.6 Ex. 3 16 0.09 1.5 2.7 Ex. 4 6 0.122.0 2.6 Ex. 5 18 0.08 1.4 3.2 Ex. 6 15 0.05 2.0 2.6 Ex. 7 10 0.07 1.52.8 Ex. 8 14 0.10 1.4 2.6 Ex. 9 11 0.14 1.2 3.2 Ex. 10 12 0.11 1.1 3.6Ex. 11 16 0.09 1.6 2.5 Ex. 12 12 0.06 1.4 2.7 Comp. 1 5 0.42 0.6 4.4Comp. 2 12 0.36 0.4 3.2 Comp. 3 18 0.35 0.3 4.1 Comp. 4 5 0.33 0.7 3.8Comp. 5 3 0.28 0.3 4.3 Comp. 6 8 0.35 0.3 4.3 Comp. 7 — — — — Comp. 8 620.06 1.8 2.4 Comp. 9 3 0.48 0.2 6.1 Comp. 10 8 0.06 0.2 5.6 Comp. 11 70.25 0.5 3.3 Comp. 12 7 0.28 0.3 3.9

TABLE 4 Characteristics Minimum Bending Tensile 0.2% Radius in UsualBending Stress Electric Strength Yield Bending WorkabilityWorkability(LD) Relaxation Conductivity (LD) Strength (R/t) afterNotching Rate (% IACS) (MPa) (MPa) LD TD (Evaluation) (TD) (%) Ex. 113.2 1005 935 0.0 0.5 good 2.4 Ex. 2 12.2 1016 915 0.0 0.0 good 2.2 Ex.3 12.4 976 905 0.0 0.0 good 2.8 Ex. 4 13.0 1025 946 0.0 0.5 good 3.1 Ex.5 13.6 980 912 0.0 0.3 good 2.2 Ex. 6 14.5 986 888 0.0 0.0 good 3.4 Ex.7 15.1 968 892 0.0 0.0 good 3.3 Ex. 8 16.2 976 965 0.0 0.0 good 3.4 Ex.9 12.4 1025 955 0.0 0.7 good 3.6 Ex. 10 12.6 1036 970 0.0 0.8 good 3.3Ex. 11 13.1 1025 955 0.0 0.5 good 2.2 Ex. 12 12.8 1034 967 0.0 0.7 good2.3 Comp. 1 13.3 1001 928 2.0 3.0 broken 4.2 Comp. 2 12.6 996 906 1.02.5 broken 3.9 Comp. 3 12.7 963 898 1.5 2.5 bad 4.2 Comp. 4 13.1 1011952 2.0 3.5 bad 5.4 Comp. 5 14.1 986 908 2.0 5.0 broken 7.6 Comp. 6 22.5842 768 1.0 2.5 bad 6.4 Comp. 7 — — — — — — — Comp. 8 12.7 928 856 2.02.5 bad 2.0 Comp. 9 15.6 1026 945 3.0 broken broken 11.6  Comp. 10 12.41114 1056  broken broken broken 6.4 Comp. 11 13.1 854 766 1.5 2.0 bad5.8 Comp. 12 12.4 962 902 2.0 4.0 broken 6.2

Furthermore, when the sheet material of the copper alloy was broken evenif R/t was 5.0, evaluation was not further carried out, and “broken” wasdescribed in the column of evaluation of the usual bending workabilityof the sheet material of the copper alloy in Table 4. In the column ofevaluation of the bending workability after notching of the sheetmaterial of the copper alloy in Table 4, “good” was described whencracks were not observed on the surface and section of the bent portionafter notching, “bad” was described when cracks were observed thereon,and “broken” was described when the sheet material was broken at thebent portion thereof. The worst results of the three test pieces wereadopted to be evaluated as “good”, “bad” and “broken”, and it was judgedthat the evaluation of “good” was acceptable.

FIGS. 5A through 5D are optical microphotographs showing the structureof the surface of the sheet material of the copper alloy before thesolution treatment, after the solution treatment at 850° C. for 10seconds, after the solution treatment at 850° C. for 30 seconds, andafter the solution treatment at 850° C. for 60 seconds, respectively, inExample 1. FIGS. 6A through 6D are optical microphotographs showing thestructure of the surface of the sheet material of the copper alloybefore the solution treatment, after the solution treatment at 850° C.for 10 seconds, after the solution treatment at 850° C. for 30 seconds,and after the solution treatment at 850° C. for 60 seconds,respectively, in Comparative Example 1 wherein the copper alloy havingthe same composition as that in Example 1 was used and the sametreatments as those in Example 1 were carried out, except that thehot-rolling reduction in the temperature range of less than 700° C. to500° C. was 20%, which was lower than that in Example 1, and that aplurality of cold rolling operations before and after the processannealing (intermediate solution treatment) at 850° C. for 120 secondswere carried out during the cold rolling before the solution treatment.As shown in FIGS. 5A through 5D, in Example 1, crystal boundary afterrolling was not clearly observed due to strong rolling before thesolution treatment, so that a uniform recrystallized grain structure wasobtained while the mean crystal grain size varies due to the variationof holding time in the solution treatment. On the other hand, inComparative Example 1, since the plurality of cold rolling operationsbefore and after the process annealing (intermediate solution treatment)at 850° C. for 120 seconds were carried out during the cold rollingbefore the solution treatment, the rolling reduction in cold rollingimmediately before the solution treatment was low, and there was a timelag in the formation and growth of recrystallized grains every rolledcrystal grain during the solution treatment, so that the uniformrecrystallized grain structure was not obtained even if the holding timewas adjusted.

As can be seen from Tables 3 and 4, in all of the sheet materials ofcopper alloys in Examples 1-12, the mean crystal grain size is in therange of from 5 μm to 25 μm, and (maximum crystal grain size−minimumcrystal grain size)/(mean crystal grain size) is not greater than 0.20.The sheet materials of copper alloys satisfy I{420}/I₀{420}>1.0 andI{220}/I₀{220}≦4.0, and have a 0.2% yield strength of not less than 850MPa. The sheet materials of copper alloys also have such an excellentbending workability that the values R/t in both of the LD and TD are notgreater than 1.0. With respect to the bending workability after notchingin the LD, which is practically important, cracks were not produced inspite of severe bending of R/t=0 in the 90° W bending test. Moreover,the sheet materials of copper alloys have such an excellent stressrelaxation resistance that the stress relaxation rate in the TD, whichis important when the sheet materials of copper alloys are used as thematerials of connectors for automobiles and so forth, is not greaterthan 5%.

On the other hand, in all of sheet materials of copper alloys inComparative Examples 1-5, although copper alloys having the samecompositions as those in Examples 1-5 were used, respectively, (maximumcrystal grain size−minimum crystal grain size)/(mean crystal grain size)was a high value which was not less than 0.28. In addition, theintensity of X-ray diffraction on the {420} crystal plane was weak, andthe intensity of X-ray diffraction on the {220} crystal plane was high,so that there were trade-off relationships between the strength andbending workability of the sheet materials of copper alloys and betweenthe bending workability and stress relaxation resistance of the sheetmaterials of copper alloys, respectively. In particular, it wasimpossible to carry out the bending after notching.

In Comparative Example 6, the content of Ti in the used copper alloy wastoo low, so that the amount of generated deposits was small. For thatreason, the strength level was low in spite of the ageing treatmentwhich was carried out on the necessary conditions for obtaining themaximum hardness. In addition, the crystal orientation having aprincipal orientation component of {420} was weak in spite of the highcold-rolling reduction of not less than 95% before the solutiontreatment. Moreover, the bending workability after notching was notimproved in spite of the low strength level. In Comparative Example 7,since the content of Ti was too high to set appropriate solutiontreatment conditions, cracks were produced during the production of thesheet material, so that it was not possible to produce any sheetmaterial to be evaluated.

In Comparative Example 8, since the solution treatment time was toolong, crystal grains were coarsened, so that it was not possible toobtain a good bending workability. In Comparative Example 9, since thesolution treatment temperature was 700° C. which was too low,recrystallization did not sufficiently proceed, so that a mixed grainstructure was produced for deteriorating all of the tensile strength,bending workability and stress relaxation resistance of the sheetmaterial.

In Comparative Example 10, since the finish rolling reduction was toohigh, the crystal orientation having a principal orientation componentof {420} was weak, and the crystal orientation having a principalorientation component of {220} was too strong, so that the bendingworkability of the sheet material of the copper alloy in the bad way wasremarkably bad although the strength thereof was high.

In Comparative Examples 11 and 12, (maximum crystal grain size−minimumcrystal grain size)/(mean crystal grain size) was high. In addition, theintensity of X-ray diffraction on the {420} crystal plane was weak, andthe intensity of X-ray diffraction on the {220} crystal plane was high,so that all of the strength, bending workability and stress relaxationresistance of the sheet materials of copper alloys were inferior tothose of the sheet material of the copper alloy in Example 1, which hassubstantially the same composition as that of the sheet materials ofcopper alloys in Comparative Examples 11 and 12.

While the present invention has been disclosed in terms of the preferredembodiment in order to facilitate better understanding thereof, itshould be appreciated that the invention can be embodied in various wayswithout departing from the principle of the invention. Therefore, theinvention should be understood to include all possible embodiments andmodification to the shown embodiments which can be embodied withoutdeparting from the principle of the invention as set forth in theappended claims.

1-5. (canceled)
 6. A method for producing a sheet material of a copperalloy, the method comprising the steps of: melting and casting rawmaterials of a copper alloy to form an ingot, said copper alloy having achemical composition which consists of: 1.2 to 5.0 wt % of titanium;optionally one or more elements which are selected from the groupconsisting of 1.5 wt % or less of nickel, 1.0 wt % or less of cobalt and0.5 wt % or less of iron; optionally one or more elements which areselected from the group consisting of 1.2 wt % or less of tin, 2.0 wt %or less of zinc, 1.0 wt % or less of magnesium, 1.0 wt % or less ofzirconium, 1.0 wt % or less of aluminum, 1.0 wt % or less of silicon,0.1 wt % or less of phosphorus, 0.05 wt % or less of boron, 1.0 wt % orless of chromium, 1.0 wt % or less of manganese, 1.0 wt % or less ofvanadium, 1.0 wt % or less of silver, 1.0 wt % or less of beryllium and1.0 wt % or less of misch metal, the total amount of these elementsbeing 3 wt % or less; and the balance being copper and unavoidableimpurities; hot-rolling the ingot in a temperature range of from 950° C.to 500° C. to form a plate of the copper alloy, by hot-rolling the ingotat a rolling reduction of not less than 30% in a temperature range offrom less than 700° C. to 500° C. after carrying out an initial rollingpass in a temperature range of from 950° C. to 700° C.; cold-rolling theplate of the copper alloy at a rolling reduction of not less than 85%;carrying out a solution treatment which holds the plate of the copperalloy in a temperature range of from 750° C. to 1000° C. for 5 secondsto 5 minutes; cold-rolling the plate of the copper alloy at a rollingreduction of 0 to 50% after the solution treatment; ageing the plate ofthe copper alloy, which is cold-rolled after the solution treatment, ata temperature of 300 to 550° C.; and finish cold-rolling the aged plateof the copper alloy at a rolling reduction of 0 to 30%.
 7. A method forproducing a sheet material of a copper alloy as set forth in claim 6,wherein said ingot is hot-rolled at a rolling reduction of not less than60% in the temperature range of from 950° C. to 700° C.
 8. A method forproducing a sheet material of a copper alloy as set forth in claim 6,wherein said rolling reduction in cold-rolling between said hot-rollingand said solution treatment is not less than 90%.
 9. A method forproducing a sheet material of a copper alloy as set forth in claim 6,wherein said solution treatment is carried out by a heat treatment whichholds said plate of the copper alloy at a higher temperature than asolid solubility curve of the copper alloy by 30° C. or more, in saidtemperature range of from 750° C. to 1000° C. for a holding period oftime which is adjusted so that the mean crystal grain size of the plateof the copper alloy after the solution treatment is in the range of from5 μm to 25 μm.
 10. A method for producing a sheet material of a copperalloy as set forth in claim 6, wherein assuming that the ageingtemperature capable of obtaining the maximum hardness in a chemicalcomposition of said copper alloy is T_(m) (° C.) and that the maximumhardness thereof is H_(m) (HV), the ageing temperature in the ageingtreatment is set to be a temperature which is T_(M)±10° C. in thetemperature range of from 300° C. to 550° C., and the ageing time in theageing treatment is set so that the hardness of the sheet material ofthe copper alloy is in the range of from 0.90 H_(M) to 0.95 H_(M) afterthe ageing treatment.
 11. A method for producing a sheet material of acopper alloy as set forth in claim 6, wherein a low temperatureannealing operation is carried out at a temperature of 150 to 450° C.after the finish cold rolling.
 12. (canceled)